PHYSIOLOGY OF THE NERVOUS SYSTEM

PHYSIOLOGY OF THE NERVOUS SYSTEM

Sept 20, 2011Group 4

Physiology of the Nervous System • Functions and Divisions• Nervous Tissue

– Neurons and neuroglia– Types– Nerve signal and transmission

• Central Nervous System– Brain and spinal cord

• Peripheral Nervous System– Types of nerves– Somatic Motor Nervous System– Autonomic Motor Nervous System

• Diseases

Functions

1. Sensory Input- sensory receptors in the skin and

organs generate nerve signals2. Integration

- brain and spinal cord interpret the data and signal nerve responses

3. Motor Output- nerve impulses from the brain and spinal cord go to the effectors

Divisions

A. Central Nervous System (CNS)- lie midline of the body- brain and spinal cord

B. Peripheral Nervous System (PNS)- project out from the CNS- cranial and spinal nerves1. afferent/ sensory2. efferent/ motor

CNS

PNS

Brain Spinal cord

Sensory Nerves(afferent)

Motor Nerves(efferent)

Somatic Sensory Nerves

Autonomic Motor Nerves

Somatic Motor Nerves

Visceral Sensory Nerves

ParasympatheticSympathetic

Nervous Tissue

A. Neurons• Dendrite- receives signals from receptors• Cell Body- contain nucleus and most of

the cytoplasm• Axon- conducts nerve impulses

• Fibers- long axons» Nerves- fibers outside the brain and spinal

cord» Tracts- fibers in the brain and spinal cord

Nervous Tissue

Types of Neurons1. Motor Neurons- (multipolar) take nerve

impulses from the CNS to muscles, organs or glands

2. Sensory Neurons- (unipolar) take nerve impulses from sensory receptors to the CNS

3. Interneurons/ Association neurons- (multipolar) convey nerve impulses between various parts of the CNS

A Typical Nerve Cell/ Neuron

Types of Neurons

Nervous Tissue

B. Neuroglia- nourish the neurons• In the brain:

1. microglia- engulf bacterial and cellular debris

2. astrocytes- provide nutrients and produce a hormone3. oligodendrocytes- form myelin4. ependymal cells- form cerebrospinal fluid

Nervous Tissue

• Outside the brain:Schwann Cells/ neurolemmocytes- provide myelin sheath to nerve fibers• Nodes of Ranvier/ neurofibril nodes-

gaps between Schwann cells• Myelin sheath- speeds up conduction

A Neuroglia

Nerve Signal Conduction

• Neurons- transmit nerve signals

• Nerve Signal- action potential, conducted by the axon


• Resting Potential– nerve cell has -70 mV of stored energy – exists because cell membrane is polarized– necessary for efficient work–Maintained through the sodium-potassium

pump

Resting Potential


• Action Potential–Process of conduction that occurs in the

axons–Begins with a stimulus• Depolarization - protein channels for Na+ open • Repolarization- protein channels for Na+ close

and channels for K+ open

Action Potential

Action Potential

Conduction of Action Potentials

• Unmyelinated Axons– Action potential at one local stimulates an adjacent

part of the axon membrane to produce an action potential

– Slow, 1m/sec in thin axons because each section of the axon must be stimulated

• Myelinated Axons– Action potential at one node of Ranvier causes an

action potential at the next node (saltatory conduction)– Faster, 100m/sec in thick axons

Conduction of Action Potentials

Refractory Period

- occurs soon as the action potential has passed by each successive portion of the axon

- Axon is unable to conduct an action potential

- Ensures one-way direction of an impulse

Transmission Across a Synapse

• Axon terminal- swelling at the tip of the axon• Synapse – region of close proximity between the

axon terminal of a neuron and a dendrite or cell body of another neuron

• Presynaptic membrane- membrane of the first neuron

• Postsynaptic membrane- membrane of the next neuron

• Synaptic cleft- small gap between the two membranes


• Neurotransmitters – Carry out transmission across a synapse– stored in synaptic vesicles in the axon terminals– e.g. Ach and NE• Excitatory neurotransmitter• Inhibitory neurotransmitter

• graded potential– small signals from a synapse



Central Nervous System

• Consists of the brain and spinal cord• Composed of:–Gray mater- contains cell bodies and short,

nonmyelinated axons–White mater- contains myelinated axons

that run together in tracts


• Meninges (sing. Meninx)- protective membranes of the spinal cord and brain– Dura mater- outer meninx; tough, white, fibrous

connective tissue that lies next to the skull and vertebrae

– Arachnoid mater- “spider-like”; consists of spider web like connective tissue

– Pia mater- deepest meninx; very thin and closely follows the contours of the brain and spinal cord


• Subarachnoid space– space in between arachnoid and pia mater–Contains cerebrospinal fluid• similar to the plasma that forms a protective

cushion around and within the CNS• Fills ventricles and hollow ventral canal of the

spinal cord

Spinal CordLong, thin tubular bundle of Nervous

System.Found inside the vertebra.Supports cells that extends the brain.Begins at the occipital bone.Main pathway for information connecting

the brain and peripheral nervous system.

Layers of Spinal Cord (Meninges)

Dura Mate

Archnoid Mater

Pia Mater

The subarachnoid space is the space which normally exists between the arachnoid and the pia mater, which is filled with cerebrospinal fluid. Normally, the dura mater attached to the skull, or to the bones of the vertebral canal in the spinal cord. The arachnoid is attached to the dura mater, while the pia mater is attached to the central nervous system tissue. When the dura mater and the arachnoid separate through injury or illness, the space between them is the subdural space.

Spinal Cord Level Numbering System

• The spinal nerves carry information to and from different levels (segments) in the spinal cord. Both the nerves and the segments in the spinal cord are numbered in a similar way to the vertebrae. The point at which the spinal cord ends is called the conus medullaris, and is the terminal end of the spinal cord. It occurs near lumbar nerves L1 and L2. After the spinal cord terminates, the spinal nerves continue as a bundle of nerves called the cauda equina. The upper end of the conus medullaris is usually not well defined.

• There are 31 pairs of spinal nerves which branch off from the spinal cord. In the cervical region of the spinal cord, the spinal nerves exit above the vertebrae. A change occurs with the C7 vertebra however, where the C8 spinal nerve exits the vertebra below the C7 vertebra. Therefore, there is an 8th cervical spinal nerve even though there is no 8th cervical vertebra. From the 1st thoracic vertebra downwards, all spinal nerves exit below their equivalent numbered vertebrae.

• The spinal nerves which leave the spinal cord are numbered according to the vertebra at which they exit the spinal column. So, the spinal nerve T4, exits the spinal column through the foramen in the 4th thoracic vertebra. The spinal nerve L5 leaves the spinal cord from the conus medullaris, and travels along the cauda equina until it exits the 5th lumbar vertebra.

1 Spinal Nerve 5 Central Canal

2 Dorsal Root Ganglion 6 Grey Matter

3 Dorsal Root (Sensory) 7 White Matter

4 Ventral Root (Motor)

BrainOverview on the parts of the brain

• Forebrain – Telencephalon

• Cerebrum– Cerebral Cortex

Frontal lobeParietal lobeTemporal lobeOccipital lobeinsula

Brocas area

• Corpus callosum• Basal Ganglia• The Limbic System

– Diencephalon

• Thalamus• Hypothalamus

–Midbrain» Tectum» Tegmentum

– Hind brain» Cerebellum» Pons» Medulla oblongata

ForebrainCerebrum

• Largest portion of the brain• Last center to receive sensory input• Carry out integration before commanding voluntary motor

responses• Carries out higher thought of processes required for learning and

memory and for language and speech• Compose of 2 hemispheres• Left and right cerebral hemisphere

• Frontal lobe- reasoning and movement• Parietal lobe- somatic sensing includes taste• Temporal- hearing • Occipital- visionBrocas area- found only in left cerebral hemisphere; motor speech area

• Cerebral cortex-thin but convulated outer layer of gray matter which covers

the cerebral hemisphere

-accounts for sensation, Voluntary movement, and all thought processes we associate with consciousness

• Limbic system– hippocampus (sea horse) and the amygdala (almond), along

with portions of the hypothalamus, thalamus, caudate nuclei, and septum function together

function: – Causes the subject to experience pain, rage, pleasure or sorrow

Corpus callosumwhite matter connects the cerebral hemisphere

Diencephalon

Hypothalamus- forms the floor of the 3rd ventricle– Maintains homeostasis by regulating hunger, sleep, thirst,

body temperature and water balance. – Also controls the endocrine system and autonomic nervous

system

Thalamus- consists of 2 masses of gray matter located in the sides and roof of the 3rd ventricle-

- integrates visual, auditory and somatosensory information and sends it to appropriate portions of the cerebrum

Mesencephalon

• Tectum- include the superior colliculi and theinferior colliculi

- visual reflexes and reaction to moving stimuli

• Tegmentum- reticular formation, periaqueductal gray matter, and the red nucleus and substantia nigra

• receives sensory information and is involved with attention, sleep and arousal, muscle tonus, movement, and various vital reflexes

Hind brain

Cerebellum- separated from the brain stem by 4th ventricle

– Receives sensory input from eyes, ears, joints and muscles

– Receives motor output from cerebral cortex where this part should be located

– Maintains posture and balance– Ensures that the muscles work together for smooth and

coordinated movements

• Pons - large bulge in the brain stem between the mesencephalon and the medulla oblongata

– believed important in the role of sleep and arousal

• Medulla oblongata- origin of the reticular formation and consists of nuclei

– control center for cardiac, vasoconstrictor, and respiratory functions.

– Reflex activities, including vomiting, are controlled by this structure of the hindbrain

Peripheral Nervous System

• Composed of:– Nerves- bundles of axons– Ganglia- swellings associated with nerves that

contain collections of cells bodies

Peripheral Nervous System

• Subdivisions:A. Afferent/ sensory system

- Somatic sensory system- serves the skin, skeletal muscles, joints and tendons; special senses

- Visceral sensory system- supplies internal organs

B. Efferent/ motor system- Somatic motor system- carries commands away from

the CNS to the skeletal muscles- Autonomic motor system- regulates activity of cardiac

and smooth muscles and glands

Types of Nerves

A. Cranial Nerves- 12 pairs, concerned with the head, neck

and facial regions of the body- Motor nerves- with only motor fibers- Sensory nerves- with only sensory fibers- Mixed nerves- with both motor and sensory

nerves

• Table, fig 8.11

Nerve Type Transmits Nerve Impulses to (Motor) or from

(Sensory)Olfactory (I) Sensory Olfactory receptors for

sense of smellOptic (II) Sensory Retina for sense of sightOculomotor (III) Motor Eye muscles (including

eyelids and lens); pupil (parasympathetic region)

Trochlear (IV) Motor Eye musclesTrigeminal (V) Mixed Teeth, eyes, skin, and

tongueJaw muscles (chewing)

Abducens (VI) Motor Eye muscles

Facial (VII) Mixed Taste buds of anterior tongueFacial muscles ( facial expression) and glands (tear and salivary)

Vestibucochlear (VIII)

Sensory Inner ear for sense of balance and hearing

Glossopharyngeal (IX)

Mixed PharynxPharyngeal muscles (swallowing) salivary glands

Vagus (X) Mixed Internal organs, external ear canal, eardrum, back of throatInternal organs (parasympathetic division), throat muscles (somatic motor division)

Spinal Accessory (XI)

Motor Neck and back muscles

Hypoglossal (XII) motor Tongue muscles

Types of Nerves

B. Spinal Nerves- 31 pairs, one of each pair is on either side of the spinal cord- grouped depending on the location on the vertebral column- cervical- thoracic- lumbar- sacral

• Table fig 8.12

Name Spinal Nerves

Involved

Function

Musculocutaneous nerves

C5-T1 Supply muscles of the arms of the anterior sides, and skin of the forearms

Radial nerves C5-T1 Supply muscles of the arms on the posterior sides, and skin of the forearms and hands

Median nerves C5-T1 Supply muscles of the forearms, and muscles and skin of the hands

Ulnar nerves C5-T1 Supply muscles of the forearms and hands, and skin of the hands

Phrenic nerves C3-C5 Supply the diaphragm

Intercostal nerves T2-T12 Supply intercostal muscles, abdominal muscles, and skin of the trunk

Femoral nerves L2-L4 Supply muscles and skin of the anterior thighs and legs

Sciatic nerves L4-S3 Supply muscles and skin of the posterior thighs, legs, and feet

Somatic Motor Nervous System

• Mostly voluntary actions• Other action are due to reflexes– Automatic involuntary responses to changes

occurring in or outside the body– Occurs quickly – Protective mechanisms essential to homeostasis• Spinal reflex• Cranial reflex

Somatic Motor System

• Some reflex used to determine if nervous system is reacting properly:– Knee-jerk reflex– Ankle-jerk reflex

Autonomic Motor Nervous System

A. Sympathetic • “fight or flight”• Important during emergency situations• Accelerates heart beat and dilates bronchi• Inhibits digestive tract (digestion is not an

immediate necessity during emergencies)• Neurotransmitter: NE

Autonomic Motor Nervous System

B. Parasympathetic• “rest and digest”/ housekeeper division• Promotes all of the internal responses we

associate with a relaxed state• Ex: contraction of the pupil of the eyes,

promote digestion, slow heart rate, lower strength of cardiac contraction

• Neurotransmitter: ACh

Diseases of the Nervous System

Term Definition Cause Effect

Bell's Palsy A form of Neuritis that involves paralysis of the facial nerve causing weakness of the muscles of one side of the face and an inability to close the eye.

Unknown. Paralysis of the facial nerve;weakness of the muscles of one side of the face;may result in inability to close the eye.

Cerebral Palsy A nonprogressive disorder of movement resulting from damage to the brain before, during, or immediately after birth.

Cerebal Palsy is attributed to damage to the brain, generally occuring before, during, or immediately after birth.

It is often associated with other neurological and mental problems. There are many causes including birth injury, hypoglycaemia, and infection.

The most common disability is a spastic paralysis.Sensation is often affected, leading to a lack of balance, and intelligence, posture and speech are frequently impaired. Contractures of the limbs may cause fixed abnormalities.Other associated features include epilepsy, visual impairment, reduced hearing, and behavioural problems.

Term Definition Cause Effect

Parkinson's Disease Degenerative disease process (associated with aging) that affects the basal ganglia of the brain.

Associated with a deficiency of the neurotransmitter dopamine.

Also associated with aging.

The commonest symptom is tremor, which often affects one hand, spreading first to the leg on the same side then to the other limbs. It is most profound in resting limbs, interfering with such actions as holding a cup.

Multiple Sclerosis A chronic disease of the nervous system that can affect young and middle-aged adults.The course of this illness usually involves recurrent relapses followed by remissions, but some patients experience a chronic progressive course.

The myelin sheaths surrounding nerves in the brain and spinal cord are damaged, which affects the function of the nerves involved.

The underlying cause of the nerve damage remains unknown.

Multiple Scerosis affects different parts of the brain and spinal cord, resulting in typically scattered symptoms. Unsteady gait and shaky movement of the limbs, rapid involuntary movements of the eyes, and defects in speech pronunciation.

• Amnesia is a state of mind wherein months or years of memories suddenly vanish. There are two types of amnesia: organic and functional. Organic amnesia is caused by damage to the brain brought about by head injuries, severe illness, senility (old age), concussions or violent blows, alcoholism, and stroke. Functional amnesia is caused by trauma (shocking event or horrifying scene) or stress. Generally, organic amnesia lasts longer than functional amnesia.

• Alzheimer disease is the most common cause of dementia. It affects more women than men, and the clinical course generally lasts approximately five years. The younger the individual is at the onset of the disease, the more severe the deficits for the patient. One famous contemporary who suffers from the disease is former U.S. President Ronald Reagan.

• Stroke is a general term for a sudden neurological event which results in the new onset of neurological symptoms.

Stroke Animation Video.flv

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PHYSIOLOGY OF THE NERVOUS SYSTEM