The Nervous System

The Nervous System

B. Pimentel, M. D.University of Makati – College of Nursing

The Nervous System

Function

1. Communication

2. Sensory Input

3. Integration

4. Mental Activity

5. Control of Muscles and Glands

The Nervous System

• Ganglia – a collection of neuron cell bodies outside the CNS.

• Nerve – a bundle of axons and their sheaths that connect the CNS to sensory receptors, muscles, and glands.

Organization

I. Central nervous system (CNS)

II. Peripheral nervous system

I. CNS

Brain

Spinal cord

Nerves

Organization

II. PNS

A. Afferent sensory nervous system

B. Efferent motor nervous system i. Somatic motor

ii. Autonomic Motor

1. Sympathetic

2. Parasympathetic

CNS

• Structural & functional center of the entire nervous system.

• Integrates sensory information: – Eyes – Ears – Smell – Taste – Touch

• Evaluates information and initiates a response

PNS

• Periphery or outer region of body

• Nerves originate from the brain

• Afferent nerves deal with all incoming sensory info.

• Efferent nerves are all outgoing motor function

PNS

PNS

• Somatic nervous system carries info. to the Skeletal muscle.

• Autonomic nervous system visceral motor (Smooth muscles, cardiac muscles, Glands, digestive, circulatory, reproductive, Urinary)

– Sympathetic - prepares body to deal with immediate threats to self "Fight or Flight".

– Parasympathetic - coordinates the body's normal resting state. "Rest and Repair".

Anatomy

Structure• Brain Average weight 1600grams (3.5 lbs.) • Spinal cord

Divisions

1. Cerebral Hemispheres (Cerebrum)

2. Diencephalon

A. Thalamus

B. Hypothalamus

C. Pineal Body (epithalamus)

Anatomy

3. Brain Stem

A. Mid brain

B. Pons

C. Medulla Oblongota

4. Cerebellum

Anatomy (Cerebrum)

Cerebral Hemispheres • Most superior part of brain.

• 83% of brain mass

• Form the largest part of the brain, occupying the anterior and middle cranial fossae in the skull and extending backwards over the tentorium cerebelli. – They are made up of the cerebral cortex, the basal ganglia,

tracts of synaptic connections, and the ventricles containing CSF.

Anatomy (Cerebrum)

• Separated from each other by median longitudinal fissure, and from cerebellum by transverse fissure; have gyri and sulci on surface

• Divided into five lobes, frontal, parietal, temporal, occipital, and insula lobes.

• Central sulcus delineates precentral gyrus and postcentral gyrus.

Anatomy (Cerebrum)

Anatomy (Cerebrum)

Anatomy (Cerebrum)

Anatomy (Cerebrum)

Supplied by three main arteries: • Anterior Cerebral Artery, Middle Cerebral Artery,

Posterior Cerebral Artery

Anatomy (Cerebrum)

Anatomy (Cerebrum)

Regions of Cerebral Hemispheres

1. Outer cortex (Gray Matter)

2. Internal (White Matter)

3. Basal Nuclei

Anatomy (Cerebrum)

Anatomy (Cerebrum)

Function of Cerebral Hemispheres (CONSCIOUS)– PERCEIVE – COMMUNICATE – REMEMBER – UNDERSTAND – APPRECIATE – INITIATE VOLUNTARY MOVEMENTS

Anatomy (Cerebrum)The Gray Matter

GRAY MATTER • Consists of neurons, cell bodies, dendrites,

unmyelinated axons, associated glial cells, & blood vessels. – Gyri - Elevated ridges – Sulcus - Shallow grooves – Fissure - Deeper grooves, separate larger regions of the

brain. • Gyri and Sulci increase surface area of gray matter three folds.

– Lobes - Deeper sulci divide each hemisphere into lobes, named after the cranial bone that overlies it.

Anatomy (Cerebrum) The Gray Matter

Anatomy (Cerebrum)The Gray Matter

Function of Gray Matter – Motor – Sensory – Association areas

• Each hemisphere is concerned with sensory and motor functions of the contralateral side of the body.

• Symmetrical in structure, but not equal in function.• No functional area of the cortex acts alone, and

conscious behavior involves the entire cortex.

Cerebrum (Motor functions)

4 motor functional areas of the cerebrum

1. Conscious control of skeletal muscle

2. Learned motor skills – Musical instruments, Typing , Writing etc.

3. Motor speech area – Broca's Area - muscles of the tongue, throat, & lips.

4. Voluntary movements of the eyes Frontal eye field


Motor areas: located in posterior part of frontal lobes, control voluntary motor function.

(i) Primary motor cortex (PMC): in precentral gyrus, pyramidal cells giving rise to long axons (corticospinal, pyramidal tracts).- Allows conscious control of movements of skeletal muscle.

(ii) Premotor cortex (PC): anterior to precentral gyrus, frontal lobe; controls learned motor skills of repetitive nature.




(iii) Brocca's area: located in one hemisphere, special motor speech area.

(iv) Frontal eye field: controls voluntary movements of the eyes.



Cerebrum (Sensory Functions)

6 Sensory area

1. Spatial discrimination

2. Integrate & analyze different somatic sensory inputs

3. Vision largest of all cortical sensory areas.

4. Hearing

5. Olfaction

6. Gustatory


Sensory areas: not confined to a single lobe; concerned with conscious awareness of sensation.

(i) Primary somatosensory cortex (PSSC): in postcentral gyrus.

- Neurons receive information from somatic sensory receptors and proprioreceptors to identify the body region being stimulated - spatial discrimination.

(ii) Somatosensory association area (SSA): posterior to PSSC, many connections with it; integrates and analyzes somatosensory inputs into comprehensive evaluation of what is being felt.


(iii) Visual areas:- Primary visual cortex (PVC)/ visual association area- Receives information from retina; interprets/evaluates visual input in light of past experiences.

(iv) Auditory areas:- Primary auditory cortex (PAC)/auditory association area- Input from cochlear receptors of inner ear; integration/perception of sound stimulus

(v) Olfactory cortex (OC): input from olfactory receptors.

(vi) Gustatory cortex: perception of taste stimuli.


Cerebrum (Association Area)

Association areas: communicate with motor cortex and other association areas to analyze, recognize, and act on sensory input; there are several of these other association areas, an example is the pre-frontal cortex.

Prefrontal cortex (PFC): intellect, cognition and personality.

Anatomy (Cerebrum)The White Matter

WHITE MATTER• Deep to gray matter• Myelinated fibers • Communication between cortex and lower CNS

centers

Anatomy (Cerebrum) The White Matter

Commissures - composed of commissural fibers connect corresponding areas of 2 hemispheres enabling them to function as a whole.

• Corpus Collosum - largest commissure

Basal nuclei - Islands of gray matter within white matter.

• Have extensive inputs from entire cerebral cortex, influence motor movements.

Anatomy (Cerebrum)

• Subcortical nuclei– Deep within the cerebrum, diencephalons, and midbrain – Involved in the control of motor functions.

• Receives input from entire cerebral cortex influences muscle movements. – Inhibits antagonistic or unnecessary movements – Some role in cognition.

Anatomy (Cerebrum)The White Matter

Structures– Caudate nucleus – Lentiform nucleus – Subthalamic nucleus – Substantia nigra

Anatomy (Diencephalon)

• Central core of forebrain• Surrounded by CHs• Includes:

– Thalamus– Hypothalamus– Epithalamus

Diencephalon (Thalamus)

• Composed of masses of gray matter held together by midline commissure, the intermediate mass; forms superolateral walls of third ventricle.

– Sorting out or editing of information occurs, impulses having to do with similar functions are relayed to appropriate area of sensory cortex and cortical association areas.

– Virtually all impulses ascending to cerebral cortex funneled through thalamus; thus thalamus is gateway to cortex.




• Afferent impulses from all senses and all parts of the body converge here and the information is sorted and sent to the proper area of the brain. – Regulation of emotion – Mediating sensation – Motor activities – Cortical arousal

– Learning & Memory


Diencephalon (Hypothalamus)

• Main visceral control center of the body

• Important to overall body homeostasis

• Located below thalamus, constitutes inferolateral walls of third ventricle; extends from optic chiasm to posterior margin of mammary bodies.




• Main visceral control center of body, has several homeostatic roles:– Center for emotional response/behavior – Body temperature regulation – Regulation of food intake – Regulation of water balance and thirst – Regulation of sleep/wake cycles – Control of endocrine system functioning

Diencephalon (Epithalamus)

• Most dorsal part of diencephalon, helps form roof of the third ventricle.

• Most noticeable landmark is pineal gland -- sleep/wake cycles

Diencephalon (Epithalamus)

Brain Stem

A. Midbrain

B. Pons

C. Medulla Oblongota

• All are gray matter surrounding white tracts. • Produce the rigidly programmed, autonomic behavoirs

necessary for our survival.

• 10 of the 12 cranial nerves are heavily involved in innervation of

the head.

Brain Stem (Midbrain)

• Located between diencephalon superiorly and pons inferiorly.– Cerebral peduncles containing pyramidal tracts; also

superior cerebellar peduncles, fiber tracts connecting midbrain to cerebellum dorsally.

– Cerebral aqueduct in midbrain connects third and fourth ventricles.



• Visual reflex that coordinates head & eye movements • Auditory relay is the reflexive responses to sound as

in the "Startle Reflex" causes you to turn your head in the direction of an unexpected sound.

– Substantia Nigra - Increases melatonin production for precursor of dopamine production.

Brain Stem (Pons)

• Bulging stem region wedged between the midbrain and medulla oblongata; dorsally forms part of the walls of the fourth ventricle; composed mostly of conduction tracts.

• Conduction tracts between higher brain centers & spinal cord

• Features: – projection fibers, middle cerebellar peduncles; several

cranial nerves originate from pons nuclei (trigemminal nerve V, facial nerve VII)

Brain Stem (Pons)

Brain Stem (Medulla Oblongata)

• Most inferior portion of the brainstem• Features:

– pyramids (large ridges) on ventral surface; inferior cerebellar peduncles; olives; number of cranial nerves associated with medulla, hypoglossal nerve (XII), glossopharyngeal (IX), vagus (X), accessory (XI), vestibulocochlear (VIII).

– plays crucial role as autonomic reflex center, contains following important visceral motor nuclei:



• Cardiovascular center controls force and rate of heart contraction.

• Vasomotor regulates blood pressure by controlling size of vessel walls.

• Respiratory center controls rate and depth of breathing.


Other controls • Vomiting • Hiccuping • Swallowing • Coughing • Sneezing

Cerebellum

• Located dorsally to pons/medulla and to intervening fourth ventricle

• Processes input received from cerebral motor cortex, various brain stem nuclei, and sensory receptors to provide the precise timing and appropriate patterns of skeletal muscle contraction required for smooth, coordinated functioning.

• Landmarks: – two cerebellar hemispheres separated by vermis medially,

convoluted surface, exhibits folia.

Cerebellum

Cerebellum

Cerebellum

Function • Process inputs received from the cerebral cortex,

various brain centers and sensory receptors to provide the precise timing and appropriate patterns of skeletal muscle contraction needed for smooth coordinated movements.

– The cerebellum continuously compares higher brains intention with the body’s performance and sends out messages to initiate the appropriate corrective measures.

Ventricles

• Fluid (CSF) filled cavities within the brain • Lined with ependymal cells

– Lateral ventricle – in each cerebral hemisphere, separated by the septa pellucida.

– Third ventricle – a midline cavity located in the center of the diencephalons between the two halves of the thalamus.

• Communicates with lateral ventricles via interventricular foramen.

Ventricles

– Fourth ventricle – supeior region of the medulla oblongata at the base of the cerebellum. Continuous with the central

canal of the spinal cord. Three openings, lateral apertures (2), and median aperture, connect it to subarachnoid space.

Ventricles

Anatomy (Spinal Cord)

• Two way conduction pathway • Major reflex center • Begins as it leaves the Foramen Magnum ends at L1 • It is protected by meninges, the spinal dural sheath,

arachnoid mater and pia mater • Thirty one pairs of spinal nerves


– Conus Medullaris – Cone shaped terminal end

– Filum Terminale – Fibrous extensions of the pia mater extends inferiorly to the coccyx for anchoring.

– Cauda Equinus – Collection of spinal nerves L2 to S4, resembles a horses tail.

Cross Sectional Anatomy (Spinal Cord)

• Gray Matter• White Matter• Two major grooves

– Anterior median fissure– Posterior median sulcus.

Cross Sectional Anatomy of the SC (Gray matter)

Gray matter/spinal roots• Appearance of an "H",

– connected by gray commissure.

• The two anterior projections– anterior (ventral) horns

• Lateral projections – lateral horns, and the

• Posterior gray matter – Posterior (dorsal) horns.

Cross Sectional Anatomy (Gray matter)

• Anterior (ventral) horns: contain nerve cell bodies of somatic motor neurons, send their axons via ventral roots of SC to skeletal muscles.

• Lateral horns: contain nerve cell bodies of autonomic (sympathetic division) motor neurons that serve visceral organs, their axons leave SC via ventral roots along with those of somatic motor neurons

Cross Sectional Anatomy of the SC(Gray matter)

• Afferent fibers carrying impulses from peripheral sensory receptors form the dorsal roots of SC

• Dorsal and ventral roots fuse laterally to form spinal nerves.

Cross Sectional Anatomy of the SC (Gray matter)

Spinal Roots

• Composed of Ventral and Dorsal roots – Ventral Roots

• Somatic motor neurons

• Largest at limb innervating cervical & lumbar regions.

– Dorsal Roots • Afferent sensory fibers from peripheral nervous system

Cross Sectional Anatomy of the SC (White matter)

• Composed of myelinated/unmyelinated nerve fibers, run in ascending and descending directions

• White matter on each side of cord can be divided into three white columns.– posterior, anterior and lateral funiculi; each funiculus

contains several fiber tracts, each tract made up of axons with similar destinations and functions.

• All spinal tracts are part of multineuron pathways that connect brain to periphery


Meninges

• Compoased of 3 connective tissue layers that lie just

external to the CNS. – Cover and protect – Protect blood vessels and venous sinus – Contains CSF – Forms partitions within skull – From external to internal

Anatomy (Meninges)

EXTERNAL INTERNAL

Dura Mater Arachnoid Pia Mater

1. Dura Mater (Tough mother) – Strongest outermost meningeal layer – Double layered – Periosteal and meningeal

• Periosteal layer – inelastic attached to inner surface of skull

• Meningeal layer – Forms the true external covering of the CNS, and continues caudally in the vertebral canal.

Anatomy (Meninges)

Dural Septa – The meningeal layer that extends inward to form flat septa that anchor the brain to the skull.

• Falx cerebri • Falx cerebelli • Tentorium cerebelli

Anatomy (Meninges)

2. Arachnoid mater (spider mother) – Loose brain covering, never dipping into sulci.

• Subdural space - Separated from the dura mater by a narrow serous cavity.

• Subarachnoid space – Beneath the arachnoid, web-like structures span this space and secure the arachnoid to the underlying pia mater. This space is filled with Cerebral Spinal Fluid (CSF). Also contains the largest blood vessels serving the brain.


Epidural Space

• Located between the Dura mater and the arachnoid. It is a fat filled cavity, excellent for fat soluble injections of anesthetics, and corticosteroids.

Anatomy (Meninges)

3. Pia Mater (Gentle Mother) – Delicate tissue, richly invested with tiny blood vessels. – Clings tightly to the brain.

Cerebrospinal Fluid (CSF)

• Fluid lining between the meninges and ventricles which surrounds the brain and spinal cord

• forms liquid cushion; helps nourish brain.

Cranial Nerves

1. Olfactory – smell, from the nasal mucosa to the olfactory bulbs

2. Optic – sensory nerve of vision

3. Occulomotor – motor to eye muscles

4. Trochlear – motor to one eye muscle

Cranial Nerves

Cranial Nerves

Cranial Nerves

5. Trigeminal – Divided into 3 branches • Opthalmic – sensory from scalp, forehead, nose, upper

eyelid, and cornea. • Maxillary – sensory from palate, upper jaw, upper teeth

and gums, nasopharynx, nasal cavity, skin and mucous membranes of the cheeks, lower eyelid, and upper lip

• Mandibular – sensory from lower jaw, lower teeth and gums, anterior tongue, mucous membrane of cheek, lower lip, skin of cheek and chin, auricle, and temporal region.

– Motor to muscles of mastication, soft palate, throat, and middle ear.

Cranial Nerves

Cranial Nerves

6. Abducens – motor to eye muscle.

7. Facial – sense of taste, motor to muscles of facial expression, throat and middle ear. Parasympathetic to submandibular, and sublingual salivary glands, lacrimal glands, and glands of the nasal cavity and palate.

8. Vestibulocochlear – hearing and balance.

Cranial Nerves

Cranial Nerves

9. Glossopharyngeal – Sensory taste, pharynx, palatine tonsils, tongue, middle ear, carotid sinus, and carotid body.

• Motor to pharyngeal muscles. • Parasympathetic to parotid salivary glands and glands of

the tongue.

10. Vagus – sensory from inferior pharynx, larynx, thoracic and abdominal organs.

• Motor to soft palate, pharynx, laryngeal muscles, and tongue muscles.

• Parasympathetic to abdominal and thoracic viscera.

Cranial Nerves

11. Accessory – motor to soft palate, pharynx, sternocleidomastoid, and trapezius.

12. Hypoglossal – motor to tongue muscles, and throat muscles.

11. Accessory – motor to soft palate, pharynx, sternocleidomastoid, and trapezius.

12. Hypoglossal – motor to tongue muscles, and throat muscles.

Cranial Nerves

PNS

• The PNS provides the link to the outside world -- both in terms of reception of stimuli and response

• Includes all neural structures outside the brain and spinal cord: – sensory receptors, peripheral nerves, their associated

ganglia, and efferent motor endings.

Functional Anatomy (PNS)

Nerve

• Parallel bundles of peripheral axons (myelinated and unmyelinated) enclosed by successive wrappings of connective tissue. – Endoneurium: a delicate layer of loose connective tissue

surrounding each axon, its myelin sheath and neurilemma.– Perineurium: coarse connective tissue layer wrapping

bundles of axons into fascicles.– Epineurium - a tough fibrous sheath enclosing bundles of

fascicles and blood vessels.


• PNS has sensory (afferent) and motor (efferent) divisions– nerves containing both sensory and motor fibers and

transmitting impulses both to and from the CNS are called mixed nerves.

• Nerves with only sensory fibers are sensory nerves, with only motor fibers are motor nerves– peripheral nerves are classified as either cranial or spinal

nerves.


Ganglia: • Collections of neuron cell bodies associated with

nerves of PNS– Ganglia associated with afferent nerve fibers contain cell

bodies of sensory neurons– Ganglia associated with efferent nerve fibers contain cell

bodies of autonomic motor neurons.

Motor endings• PNS elements that activate effectors by releasing

neurotransmitters.

Anatomy (Neurons)

• Made up of a cell body and Axon(s) and one or more dendrites.

• Excitable cells that conduct impulses that make possible all nervous system functions.

• Cell body - is largest part of cell resides in CNS

Anatomy (Neurons)

Anatomy (Neurons)

Dendrites - Branch extensively from cell body. Distal ends are receptors. Conduct impulses to the cell body.

Axon – Single process, extends from a tapered hillock of the cell body. Conducts impulses away from cell body – Side branches called Axon Collaterals – Distal tips from branches are called Telodendria that

terminate into a Synaptic Knob Contains mitochondria and numerous vesicles for neurotransmitters.

Classification of Neurons

• Multipolar - many dendrites and a single axon, most are found within CNS and motor neurons.

• Bipolar - 2 processes a dendrite and an axon, located in some sensory organs

– i.e. retina of eye, and nasal cavity.

• Unipolar - single process extending from the cell body, this process divides into two branches a short distance from the cell body.

– One branches to the CNS, and the other to the periphery and has dendrite like sensory receptors the two branches function as a single axon.

Neuroglia Cells

Neuroglia cells more numerous than neurons in CNS.

• Major supporting cells for the CNS. • Formation of a permeability barrier the blood and the

neurons• Phagocytize foreign substances. • Produce CSF• Form myelin sheaths around neurons

Neuroglia Cells

1. Astrocytes

2. Ependymal cells

3. Microglia

4. Oligodendrocytes

Neuroglia Cells (Astrocytes)

• Star shaped cytoplasmic extensions that spread out to form process which cover blood vessels, neurons, and pia mater.

• Extensive cytoskeleton of microfilaments that enables them to form a supporting network for blood vessels and neurons.

• Regulates the extracellular composition of brain fluid.

Neuroglia Cells (Astrocytes)

• Promotes the formation of tight junctions, together with the endothelial cells of the blood vessels forms a Blood Brain Barrier-, which determines which substances can pass from the blood into the nervous system.

• Control the composition of the interstitial fluid by regulating the concentration of ions and gases and by recycling neurotransmitters.

Neuroglia Cells (Ependymal Cells)

• Line the ventricles of the brain and the central canal of the spinal cord.

• Choroid Plexuses – formed by specialized ependymal cells and blood vessels, these are located in certain regions of the ventricles, secretes CSF that circulates through the ventricles.

• Ciliated free surface assists in the movement CSF through the cavities of the brain.

Neuroglia Cells (Microglia)

Specialized macrophages, that becomes mobile and phagocytic in response to inflammation.

Phagocytize necrotic tissue, microorganisms, and foreign substances that invade the CNS.

Neuroglia Cells (Oligodendrocytes)

• Cytoplasmic extensions that surround axons wrap around many times and form a myelin sheath.

Myelin

• Phospholipid that insulates axons electrically.

• Action potentials propagate quicker along myelinated axons versus unmyelinated axons.

• The membrane is tightly coiled around the axon with interruptions every 0.3 to 1.5mm these are called NODES OF RANVIER

Plasma Membrane

• High concentration extracellularly – Sodium – Chloride

• High concentration intracellularly – Potassium – Negatively charged particles

• Proteins • Molecules containing phosphorous

Concentration Differences

1. Sodium-Potassium pump

• Active transport against the concentration gradient. Approximately 3 sodium ions and two potassium ions are

transported per ATP molecule.

Concentration Differences

2. Permeability characteristics of the plasma membrane

• Nongated ion channels – are always open and responsible for the resting membrane permeability.

• Gated ion channels – open and close due to a stimulus.– Ligand gated ion channels – molecule that binds to a receptor.

Open and close in response to a ligand binding to a receptor.

– Voltage gated ion channels – open and close in response to small voltage differences across the membrane.

Resting Membrane Potential

The potential difference across the plasma membrane in a resting state is -70 to -90 millivolts.


• The number of charged molecules and ions inside and outside the cell is nearly equal.

• The concentration of potassium is higher inside than outside the cell, and the concentration of sodium is higher outside than inside the cell.

• The plasma membrane is 5o to 100 times more permeable to potassium than to other positively charged ions such as sodium.


• The plasma membrane is impermeable to large intracellular negatively charged molecules such as proteins.

• Potassium ions tend to diffuse across the plasma membrane from inside to the outside of the cell.

• Because negatively charged molecules cannot follow the positively charged potassium ion, a small negative charge develops just inside the plasma membrane.


• The negative charge inside the cell attracts positively charged potassium. – When the negative charge inside the cell is great enough to

prevent additional potassium ions from diffusing out of the cell through the plasma membrane, an equilibrium is established.


• The charge difference across the plasma membrane at equilibrium is reflected as a difference in potential, which is measured in millivolts.

• The resting membrane potential is proportional for potassium to diffuse out of the cell but not to the actual rate of flow for potassium.


• At equilibrium there is very little movement of potassium or other ions across the plasma membrane.

Action Potential

Action Potential

Action Potential

Action Potential

Action Potential

Synapse

A junction between two cells where an action potential in one cell can cause the production of action potentials in another cell.

• Presynaptic cell - carries the action potential towards a synapse.

• Postsynaptic cell - carries the action potential away from the synapse.

Synapse

Synapse

Synapse

Postsynaptic Potentials

• Excitatory Postsynaptic Potential (EPSP) - depolarization of the postsynaptic membrane occurs due to neurotransmitters and their receptors. This is a local depolarization, that may reach threshold and produce an action potential and a response from the cell.

Postsynaptic Potentials

• Inhibitory Postsynaptic Potential (IPSP) - occurs when the combination of neurotransmitter and its receptor results in a hyperpolarization of the postsynaptic membrane, the response is inhibitory. – IPSP decrease the likelihood of producing action potentials

by moving the membrane potential farther from the threshold.

Neurotransmitters

The means by which each neuron communicates with others to process information and send messages.

1. Chemical synapses – Specialized structures at terminal ends of axons and dendrites to release and receive chemical neurotransmitters.

Neurotransmitters

2. Synaptic Vesicles – pre and postsynaptic membranes contain these tiny sacs, which contain many different neurotransmitters in the pre synaptic axon, and the postsynaptic dendrite contains many different receptor sites for the different neurotransmitters.

3. Synaptic cleft – separates postsynaptic and pre synaptic neurons, fluid filled space approx. 30 to 50nm. Unidirectional communication between axons.

Neurotransmitters

1. Acetylcholine – First to be identified – Used in neuromuscular junctions and the CNS– Degraded by acetylcholinesterase.– Prolonged exposure of acetylcholine will result in neural

frying. • Nerve gas

• Insecticides

• Snake venom

Neurotransmitters

2. Dopamine – CNS Autonomic system – Involved in emotions/moods and regulation of motor control.– Parkinson’s is a degeneration of dopamine axons. – Schizophrenia may be an increase in dopamine release and

axons.

Neurotransmitters

3. Norepinephrine – Several areas of the CNS and the sympathetic division of

the autonomic nervous system. – Regulates sympathetic effectors; in the brain, involved in

emotional responses. Arousal, dreaming. – Release enhanced by amphetamines (speed), removal from

postsynaptic cleft by cocaine.

Neurotransmitters

4. Serotonin – CNS – Induction of sleep, sensory perception, temperature

regulation, and control of mood. – Drugs that block the reuptake of serotonin relieve anxiety

and depression. May be responsible

Neurotransmitters

5. Histamine – Brain – Involved in emotions, and regulation of body temperature,

and water balance. – Also released by white Blood Cells causing edema

(swelling) and smooth muscle constriction

Neurotransmitters

6. Substance P – PNS – Pain transmitter

7. Enkephalins – CNS, retina, and intestinal tract. – Acts like opiates to block pain.

8. Endorphins – CNS, retina, and intestinal tract – Memory, learning, sexual activity, temperature control. – Decreased amount leads to depression.

The End

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The Nervous System