Nervous System

Functions of the Nervous System

• Sensory Input– Monitors changes

(stimuli) inside and outside the body

• Integration– Processes and interprets

sensory input to decide what should be done

• Motor Output– Supplies response by

activating muscles or glands

Nervous System Divisions

• Central Nervous System (CNS)– Includes the Brain and Spinal Cord

• Peripheral Nervous System (PNS)– Includes Spinal nerves & Cranial nerves

Further Breakdown of PNS

• Sensory (afferent) Division– Sends impulses to the CNS from sensory

receptors in body– Somatic sensory fibers: messages from skin,

muscles and joints– Visceral sensory fibers: messages from

internal organs

• Motor (efferent) Division– Carries impulses from CNS to effector organs

(muscles and glands) to cause a response

SAMESensory = Afferent

(comes first, body brain)Motor = Efferent

(comes second, brain body)

Further Breakdown of Motor Division

• Somatic System– Voluntary control of skeletal muscles

• Autonomic System– Involuntary body responses, such as smooth

& cardiac muscles, and glands

Nervous Tissue

• Made up of two types of cells– Supporting Cells: these structures do not

directly transmit any signals, but they help the neurons to function properly; aka “glia”

– Neurons: actually pass signals

Supporting Cells

• Neuroglia: supporting cells (glia) lumped together (term is commonly used to reference all types of supporting cells)

Neuroglia Cells

Neuron Cell Body

Types of Supporting Cells in CNS

• Astrocytes– Form barrier between capillaries and neurons– Help control chemical environment in brain– “To Make Mice Smarter, Add A Few

Astrocytes!”– Scroll to bottom of website to see how astrocytes communicate

• Microglia– Dispose of debris, such as dead brain cells

and bacteria (immune system)

Each astrocyte has its own territory (they don't overlap), and each may interact with

several neurons and hundreds to thousands of

synapses to properly integrate information.

"End-feet" connect to blood vessels in the brain. By signaling blood vessels

to expand or narrow, astrocytes regulate local blood flow to provide oxygen and nutrients to neurons in

need.

Astrocytes can release gliotransmitters (like glutamate) by

exocytosis to send signals to neighboring neurons.

Astrocytes

Neurons

Types of Supporting Cells in CNS

• Ependymal– Lines cavity of brain & spinal cord– Circulate cerebrospinal fluid

• Oligodendrocytes– Wrap around nerve fibers, forming myelin

sheaths

Types of Supporting Cells in PNS

• Schwann cells: form myelin sheaths in PNS

• Satellite Cells: protective, cushioning cells in PNS

Neuroglia Cells

Neuron Cell Body

Parts Of A Neuron

• Cell Body: metabolic center, contains rough ER (Nissl substance) and neurofibrils (maintain shape)

• Dendrites: convey incoming messages toward cell body

Parts Of A Neuron

• Axons: conduct outgoing messages away from cell body (has only one originating at axon hillock)

• Axon Terminal: branching at end of axon which contain neurotransmitters

Parts Of A Neuron

• Synaptic Cleft (Synapse): gaps between neurons

• Myelin Sheath: protects and insulates nerve fibers (axon), increases rate of nerve impulses; made of proteins and lipids

Parts Of A Neuron

• Schwann cells: cells forming myelin sheath in PNS– CNS =

oligodendrocytes

• Nodes of Ranvier: gaps between Schwann cells on axon

Did you know Einstein’s brain was STOLEN? Here the story here.

FYI: Multiple Sclerosis

• Myelin sheaths around the fibers are destroyed, and converted into hardened sheaths called scleroses

• Person loses ability to control muscles

Neuron Classification

• Functional– Sensory (afferent): carry impulses from

sensory receptors to CNS– Motor (efferent): carry impulses from CNS to

body– Association (interneurons): connect motor and

sensory neurons in neural pathways of CNS

Neuron Classification

• Structural– Multipolar: several

extensions from cell body (common for motor neuron)

– Bipolar: one axon and one dendrite from cell body (common for interneurons)

– Unipolar: single process from cell body, process divides (common for sensory neuron)

Central Nervous System

http://www.youtube.com/watch?v=snO68aJTOpM

Central Nervous System

…also called the CEREBRUM

Brain Characteristics

• Gyri: elevated ridges of tissue (gyrus is singular)

• Sulci: shallow grooves separating gyri (sulcus is singular)

• Fissures: deep grooves separating large regions of brain

• Lobes: separations of hemispheres of brain

Senses & Controls of Brain - Cerebrum

• White matter: collections of myelinated nerve fibers, usually found in deeper brain matter; carries the impulses (axons)

• Gray matter: collections of UNmyelinated nerve fibers and cell bodies; usually found in the outer areas; contains the neuron cell bodies

Cerebrum

• The cerebrum is divided into right and left hemispheres by the longitudinal fissure

• Controls consciousness

• Senses and motor control occurs here!

• Each hemisphere divided into 4 lobes

Funny thing about the brain…

• The somatic sensory area (cortex)– Where your senses are picked up & processed– Upside down

• Signals from body parts toward the head are picked up at the base of the area, while signals from lower (inferior) body parts are picked up at the top of the area

– Crossed pathways• Left side of the sensory area receives impulses from

the right side of the body, and vice versa

Funny thing about the brain…

• The primary motor area (cortex)– Responsible for sending out signals for

movement– Also upside down with crossed pathways

Senses & Controls of Brain - Cerebrum

• Occipital Lobe: contains visual sense

• Temporal Lobe: contains smell & auditory senses– Also includes the

hippocampus, which is responsible for long-term memory (including forming new memories about events) and spatial navigation

Frontal Lobe…• Broca’s area: ability to

speak (vocalize), usually more developed in left hemisphere

• Language comprehension area: word meanings

Broca’s Area

Senses & Controls of Brain - Cerebrum

Language Comprehension

Senses & Controls of Brain - Cerebrum

• Speech Area (aka Wernicke’s Area)– located at the junction

of the temporal, parietal, and occipital lobes

– Allows one to context spoken words (use them correctly)

– Usually more developed in left hemisphere

Speech Area

Senses & Controls of Brain - Cerebrum

• The Corpus Callosum is a very large nerve fiber tract (bundle) that connects the cerebral hemispheres & allows them to communicate

Cerebellum

• Provides timing for skeletal muscle activity

• Controls balance and equilibrium

• Are you clumsy? Uncoordinated? Blame your cerebellum!

Sections of Diencephalon

• Thalamus– Relay station for

sensory impulses up to correct part of sensory cortex

– Like an e-mail server… sends the message to the right place!

Sections of Diencephalon• Hypothalamus

– Helps regulate body temp, water balance, and metabolism (homeostasis)

– Involved with emotions; contains thirst, appetite, sex, pain, fear, rage, affection, and pleasure centers

Sections of Diencephalon– Regulates the

pituitary gland (attached)

– Mammillary body (smell recognition) and optic chiasma (optic nerves crossing) attached

ANATOMY HUMOR…

The hypothalamus is one of the most important parts of the brain,

involved in many kinds of motivation, among other functions.

The hypothalamus controls the “Four F’s”: fighting, fleeing, feeding,

and mating.

-Unknown psychology professor in neuropsychology course

Sections of Diencephalon

• Epithalamus– Pineal body: assists in

biological clock (daily/seasonal/life cycles) by releasing melatonin

– Choroid plexus: forms cerebrospinal fluid (there is also another one in the brainstem)

Sections of Brainstem• Midbrain

– Conveys ascending and descending impulses

• Pons– Conveys ascending

and descending impulses

– Helps to regulate breathing

Sections of Brainstem• Medulla Oblongata

– Conveys ascending and descending impulses

– Regulates autonomic activities such as heart rate, blood pressure, breathing, swallowing, vomiting, defecation, sneezing, coughing… the list goes on

• As soon as it passes out of the skull (through the foramen magnum), the brainstem is then known as the spinal cord

Meninges of the CNS

• Dura Mater: thick, outer-most

• Arachnoid: spiderweb-like• Pia Mater: innermost,

clings to brain

Cerebrospinal Fluid

• A watery broth that circulates and protects the brain & spinal cord from trauma

• Formed by choroid plexuses, circulated by ependymal cells

• A very weak salt solution with low amounts of protein (200 mL total; 135-150 mL around the brain)

• Any change in composition (levels of protein, presence of blood, glucose levels) may be a sign of meningitis, tumors, infection, or something else

• Tested through a spinal tap

• Ventricles– Set of structures

(openings) containing CSF in the brain

– Drains into the central canal of the spinal cord

Central Nervous System

• Brain• Spinal Cord

– Extends from medulla oblongata (at foramen magnum) to the T12 vertebrae (last thoracic vertebrae)

– Below T12 is the cauda equina (a collection of spinal nerves)

Spinal Cord – 3 Basic Parts

• Inner gray matter columns– Mostly cell bodies

• Outer white matter columns– Conduction tracts– Composes most

of spinal cord

• Central canal filled with CSF

Peripheral Nervous System

• Composed of Nerves: bundles of nerve fibers

• Neuron fibers surrounded by connective tissue (work similar to muscle fibers!)

• Two Types of Peripheral Nerves: Spinal & Cranial Nerves

Nerves

• Endoneurium surrounds each fiber

• Groups of fibers are bound into fascicles by perineurium

• Fascicles are bound together by epineurium

Spinal Nerves

• Spinal Nerves– 31 originating from

spinal cord– Named for segments

• Cervical – 8 (not 7)• Thoracic – 12• Lumbar – 5• Sacral – 5• Coccygeal – 1 (not

4)• Spinal nerves continue on

to form the rest of the nerves in your body!

Nerves

• Endoneurium surrounds each fiber

• Groups of fibers are bound into fascicles by perineurium

• Fascicles are bound together by epineurium

Nerves

• Cranial Nerves– 12 originating from

brainstem• Olfactory – smell• Optic – vision• Oculomotor – eye lens

shape, pupil size (moving eyeball)

• Trochlear – follow moving objects with eye

Nerves

• Trigeminal – skin senses from face, chewing muscles

• Abducens – roll eye laterally• Facial – facial expression muscles, lacrimal

(tear) and salivary (spit) glands, taste• Vestibulocochlear – sense of balance, hearing• Glossopharyngeal – swallowing and saliva

production

Nerves

• Vagus – sense & motor of pharynx & larynx• Accessory – activate sternocleidomastoid and

trapezius muscles (turn neck, shrug shoulders)

• Hypoglossal – control tongue movements

Transmitting Impulses

• Nerve impulses have a domino effect

• Each neuron receives an impulse and must pass it on to the next neuron– Dendrites pick up the impulse– Shuttled through the axon– Transmitted to next neuron at axon terminal

Sending The Signal

Impulse through a neuron…• Polarized: the neuron at rest

– More sodium ions outside the cell, less potassium ions on the inside (in comparison to the # of Na ions on outside)

– Sodium/Potassium pumps keep it this way

– Because the abundance of sodium ions outside the cell is way higher than the abundance of potassium ions on the inside, we would say that there is a partially positive charge on the outside of the cell, and a partially negative charge on the inside of the cell

– This balance of charges is called the Resting Potential

Through a neuron…

• Depolarization: A stimulus comes along, and Na+ moves into the membrane

– The stimulus (neurotransmitter) opens sodium channels, allowing Na+ to rush in

– The neuron continues to open channels all along membrane

Through a neuron…

• Action Potential: The depolarization wave continues to move down the membrane– Once this process is started, it continues

to move all the way down the membrane

• Once you “pop”, you can’t stop!

Through a neuron…

• Repolarization: K+ ions move outside, and Na+ ions stay inside the membrane

– Potassium channels on inside of membrane open to allow K+ to move out

Through a neuron…

• Refractory period: Everything gets put back to normal… K+ returns to inside, Na+ returns to outside

– All thanks to Na+/K+ pump– Can’t respond to another stimulus during this

period

• The cell is then returned to the polarized state until another impulse comes along

• Remember: the process takes less time if it has a myelin sheath around the neuron processes!

• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.html

Between neurons…

• Remember that action potential that was created? Well, eventually, it reaches the end of the axon (axon terminals)

• When it does, it goes through steps to pass the signal on to the next neuron…

Between neurons

• Calcium gates in axon terminals open, allowing Ca+2 in

• Due to Ca+2 entering the axon terminal, a specific neurotransmitter gets released

• Neurotransmitter diffuses across synapse

• Neurotransmitter binds with specific receptors on the next neuron

Returning to normal

• The neurotransmitter can do one of two things…– If received by another neuron, it will open Na+

gates on the next neuron, beginning a new action potential on the new neuron

– If received by some body part, it will stimulate some sort of change (muscles, glands, etc.)

• After neurotransmitter does its job, the receptor releases it back into synapse, and finds its way back to the neuron so it can be re-released

• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter14/animation__chemical_synapse__quiz_2_.html

• There are approximately 20 known neurotransmitters

Types of neurotransmitters

• Acetylcholine (ACh) – voluntary movement of muscles

• Norepinephrine – wakefulness or arousal• Dopamine – motivation, pleasure, associated

with addiction and love• Serotonin – memory, emotions, temperature

regulation• Histamine – wakefulness• Endorphins – natural pain killer

** Many neurotransmitters also have hormonal effects.

Nervous System Conditions

Meningitis

• Inflammation of the meninges

• Can then spread to actual nervous tissue of CNS, and inflame the brain (encephalitis)

Hydrocephalus

• CSF accumulates (most commonly) because of an obstruction

• “Water on the Brain”

Myelitis

• Swelling of the spinal cord

• Disrupts CNS functions linking the brain and limbs

Multiple Sclerosis

• Myelin sheaths around the fibers are destroyed, and converted into hardened sheaths called scleroses

• Person loses ability to control muscles

• Victims experience muscle weakness, abnormal muscle spasms, and difficulties in movement, coordination, & balance

Cerebrovascular Accident

• Commonly called a stroke

• The result of a ruptured blood vessel supplying a region of the brain

• Brain tissue supplied with oxygen from that blood source dies

• Loss of some functions or death may result

Alzheimer’s Disease

• Progressive degenerative brain disease

• Structural changes in the brain include abnormal protein deposits, twisted fibers within neurons, and atrophy of the brain

• Victims experience memory loss, irritability, confusion, and hallucinations

Parkinson’s Disease

• Loss of dopamine-secreting cells

• Causes other transmission problems, which leads to symptoms

• Victims experience tremors, rigidity, and gait issues (posture and walking)

Traumatic Brain Injury (TBI)

• Concussion– Slight or mild brain injury– Bleeding & tearing of nerve fibers happened– Recovery likely with possible memory loss

• Contusion– A more severe TBI– Nervous tissue destruction occurs– Nervous tissue does not regenerate

Traumatic Brain Injury (TBI)

• TBI can often result in either temporary or permanent amnesia– Anterograde amnesia: new events are not

transferred to the permanent as long-term memory

– Retrograde amnesia: inability to recall memories of the past