Nervous System

Review

Functions of the Nervous System

• Receive sensory input (gather info)

• Integration (interpret input)

• Maintain homeostasis (monitor change)

• Mental activity (consciousness, memory & thinking)

• Control of skeletal muscles (movement).

Divisions of the Nervous System

• CNS– Develops from embryonic neural tube

– Consists of brain & spinal cord

– Integrating & command center (interprets sensory input)

• PNS– Nerves outside brain & spinal cord

– Refer to question # 22 for cranial & spinal nerves

Divisions of the Nervous System

• PNS– Afferent division – towards CNS (sensory) –

somatic & visceral sensory fibers (sense organs)– Efferent division – away from CNS (motor); 2

subdivisions:a. somatic motor nervous system – voluntary – control of

skeletal musclesb. autonomic nervous system – involuntary – controls

cardiac & smooth muscle & glands; 2 subdivisions: 1. sympathetic division – prepares one for physical

activity – “fight or flight” 2. parasympathetic division – activates functions that

are associated with the body

Divisions of the Nervous System

Cells of the Nervous System

• Nerve– a bundle of axons in the PNS that functions to conduct

action potentials to & from the CNS (called tracts in CNS).

– There are no cell bodies in nerves.

• Neuron – A nerve cell with cell body, axon & dendrites.

– Axons carry impulse away from the cell body

– Dendrites carry impulse towards cell body.

Cells of the Nervous System

• Sensory (afferent) nerve– Carry impulses to CNS from sense organs– Cell bodies are outside the CNS.

• Motor (efferent) nerve– Carry impulses from CNS to muscles and glands– Cell bodies are always in CNS

• Mixed nerves– Contain both sensory and motor nerves.

• Interneurons or association neurons– Neurons that provide connections between sensory

and motor neurons, as well as between themselves.

Examples

• Sensory (afferent) nerve– Olfactory sensory neurons– Mechanoreceptors– Chemoreceptors

• Motor (efferent) nerve– Somatic motor neurons (innervate skeletal

muscles)– Visceral motor neurons (innervate cardiac &

smooth muscle)

• Mixed nerves – Median nerve at the wrist– Spinal nerves

3 Neuron Types & Functions

• Multipolar– A type of neuron that possesses a single (usually long) axon

and many dendrites, allowing for the integration of a great deal of information from other neurons

– Most efferent neurons and most CNS neurons.

• Bipolar – A single axon and dendrite arise at opposite poles of the cell

body

– Found only in sensory neurons, such as in the retina, olfactory and auditory systems.

• Unipolar

– Presence of only a single axon, branching at the terminal end;

most afferent neurons.

5 Different Neuroglia & Their Functions

• Astrocytes– Star-shaped– Anchor neurons to capillaries– Form barrier between capillaries and neurons (blood brain

barrier)– Control chemical environment of brain.

• Microglia – Spider-like phagocytes– Dispose of debris– Protect CNS from infection.

• Ependymal cells – Line cavities of the brain and spinal cord– Beating cilia circulate cerebrospinal fluid

5 Different Neuroglia & Their Functions

• Oligodendrocytes – Produce myelin sheath around nerve fibers

in the central nervous system– Unable to transmit nerve impulses– Never lose their ability to divide– Most brain tumors are gliomas - tumors

formed by neuroglia• Schwann cells • Form myelin sheaths around axons, or enclose

unmyelinated axons, in PNS

Ganglia

• Groups of neuron cell bodies in the PNS • Preganglionic neurons are autonomic neurons

whose cell bodies are located in the CNS & that synapse with postganglionic neurons.

• Postganglionic neurons are autonomic neurons whose cell bodies are located outside the CNS and that receive synaptic stimulation from preganglionic autonomic neurons.

Gray Matter vs. White Matter

• Gray matter – Groups of neuron cell bodies and their dendrites

– Composed of unmyelinated neurons

– Distributed at the surface of the cerebrum & cerebellum, as well as in the depth of the cerebral, cerebellar, and spinal white matter

– Function of gray matter is to route sensory or motor stimulus to interneurons of the CNS for creation of response to stimulus through chemical synapse activity.

Gray Matter vs. White Matter

• White matter

– Composed of myelinated nerve cell processes, or axons, which connect various gray matter areas (the locations of nerve cell bodies) of the brain to each other and carry nerve impulses between neurons

– Forms the bulk of the deep parts of the brain and the superficial parts of the spinal cord

• Generally, white matter can be understood as the parts of the brain and spinal cord responsible for information transmission (axons)

• Whereas, gray matter is mainly responsible for information processing (neuron bodies)

Propagation of Action Potentials

• Resting membrane potential– Charge difference across the membrane of a resting

cell (slightly (+) on the outside and (–) on the inside)

– Higher concentration of Na+ on the outside & higher concentration of K+ on the inside

• Action potential – Charge reversal (resulting from Na+ moving into the

cell) & return to its resting level (result of Na channels closing & K channels opening - K+ moving out of the cell)

Propagation of Action Potentials

• Depolarization– Occurs when Na+ enter the cell & cause the

inside of the cell to become more positive and the outside more negative.

• Repolarization – A change in charge back to the resting

membrane potential – Occurs when Na channels close & K channels

open & K+ move out of the cell

Propagation of Action Potentials

• Mitochondria – Produce the large amount of energy (ATP)

required by the neuron

Proprioceptors

• Nerves that innervate the joints & tendons & provide information about the position of the body & its various parts.

5 Components of a Reflex Arc

• Sensory receptor (ex: skin)• Sensory or afferent neuron• Integration center (association neuron in CNS)• Motor or efferent neuron• Effector organ (ex: muscle or gland)

Central Nervous System (CNS)

• Brain • Spinal cord

4 Major Regions of Brain

• Cerebrum• Diencephalon• Brain stem • Cerebellum

Brain Stem

• Midbrain– Cerebral peduncles (2 bulging fiber tracts) convey ascending &

descending impulses– Corpora quadrigemina (4 rounded protrusions) – reflex centers

for vision and hearing • Pons (Bridge)

– Involved in control of breathing • Medulla oblongata

– Important control center for• Heart rate control• Blood pressure regulation• Breathing• Swallowing• Vomiting

Diencephalon

• Thalamus– Relay station for sensory impulses & sensory cortex

• Hypothalamus– Helps regulate body temperature

– Controls H2O balance

– Regulates metabolism

– Part of limbic system – emotions

– Pituitary gland hangs from anterior floor by slender stalk

– Regulates pituitary gland

– Produces 2 of its own hormones

Diencephalon

• Epithalamus– Forms roof of 3rd ventricle– Houses the pineal body which

• May influence onset of puberty• Appears to play a major role in sexual development,

hibernation & migration in animals, metabolism, and seasonal breeding.

• Produces melatonin, which is stimulated by darkness and inhibited by light

– Includes the choroids plexus that forms cerebrospinal fluid (CSF)

– Involved in the emotional & visceral response to odors

Cerebrum

• Frontal lobe

• Parietal lobe

• Occipital lobe

• Temporal lobe

Cerebrum

• Frontal lobe– Primary motor area– Motivation, aggression, mood & olfactory

(smell) reception– Language comprehension (word

meanings)– Broca’s area – located in only one

hemisphere usually the left• Language processing• Speech production• Comprehension

Cerebrum

• Parietal lobe– Somatic sensory area for touch, pain, &

temperature – Gustatory area – taste– Wernicke’s area (usually in left

hemisphere) – sensory speech area• Involved in understanding &

comprehension of spoken language

Cerebrum

• Occipital lobe– Visual area

• Temporal lobe– Auditory area – hearing

– Olfactory area – smell

– Plays an important role in memory

– Abstract thought & judgment

Main Fissures of Cerebrum

• Longitudinal fissure– Separates the left & right cerebrum.

• Parieto-occipital sulcus – Separates the parietal lobes and the

occipital lobes in both hemispheres.

Gyri vs. Sulci

• Gyri – Rounded elevations or folds on the

surface of the brain.

– Increase the surface area for neurons.

• Sulci – Grooves on the surface of the brain

between the gyri.

Functional Areas of Cerebral Cortex

• Olfactory area– Smell

• Language comprehension area– Word meanings

• Motor speech area (Broca’s Area) – Ability to speak or say words properly

• Frontal association area – Carrying out “higher” functions such as

perception, decision-making as well as controlling thoughts

Functional Areas of Cerebral Cortex

• Premotor area – Muscle action is learned through practice

• Primary motor area – Sends impulses to skeletal muscles

• Somatic sensory area – Receives impulses from the body’s sensory

receptors & interprets them

• Gustatory area – Taste

Functional Areas of Cerebral Cortex

• Speech/Language area (Wernicke’s area)

– Allows one to sound out words

• General interpretation area – Interpretation of input

• Visual area – Sight

• Auditory area – Hearing

Corpus Callosum

• A large, thick nerve fiber tract connecting the 2 cerebral hemispheres for communication.

• White matter

• Connects the 2 cerebral hemispheres for communication

Right vs. Left Hemispheres

• Important b/c some functional areas are only in one hemisphere.

• The right side of the brain controls the left side of the body and vice versa.

Meninges vs. Ventricles

• Meninges – A series of 3 connective tissue membranes

• Dura mater

• Arachnoid mater

• Pia mater

– Surround & protect the brain & spinal cord

• Ventricles – One of 4 cavities in the brain filled w/

cerebrospinal fluid.

Cerebellum Functions

• Provides involuntary coordination of body movements (balance & equilibrium)

• Monitors body position & corrects (“autopilot”)

• Connects to inner ear & eye

• Involved in learning a motor skill such as riding a bicycle or playing a piano

3 Membranes of CNS• Dura mater

– Consisting of the periosteal (attached to surface of the skull) and meningeal (outer covering of the brain) layers

• Arachnoid mater – Middle covering, attached to the inside of the

dura, surrounds the brain and spinal cord but does not line the brain down into its sulci.

• Pia mater – Internal layer, clings to the surface of the

brain.

Cerebrospinal Fluid

• Fills the brain ventricles, the central canal of the spinal cord, and the subarachnoid space.

• Bathes the brain & spinal cord, providing a protective cushion around the CNS.

Peripheral Nervous System (PNS)

• Cranial nerves – Peripheral nerve originating in the brain– Part of the PNS– Consists of 12 pairs– Some are only sensory, & some are only somatic

motor, whereas others have more than one function– Cranial nerves with both afferent & efferent

functions are called mixed nerves.

• Spinal nerves – Arise along the spinal cord from the union of the

dorsal roots and ventral roots– All are mixed nerves.