The nervous system/special senses

Functions of the nervous system

sensory input, integration, motor output

sensory input

gathering information by sensory receptors that monitor changes

Stimuli

changes occurring inside or outside the body

Integration

nervous system processes and interprets sensory input, and decides if an action is needed

motor output

a response, or effect, that activates muscles/glands

Two classifications of nervous system

central nervous system, peripheral nervous system

functional classifications of nervous system

sensory (afferent) division, motor (efferent) division

Central nervous system organs

brain, spinal cord

central nervous system function

integration, command center, interprets incoming sensory ingo, issues outgoing instructions

peripheral nervous system

nerves extending from brain and spinal cord

spinal nerves

carry impulses to and from spinal cord

cranial nerves

carry impulses to and from brain

peripheral nervous system functions

serve as communication lines among sensory organs (brain/spinal cord), and glands or muscles

Sensory (afferent) division

nerve fibers that carry information TO the central nervous system

somatic sensory (afferent) fibers

carry info from the skin, skeletal muscles, and joints

Visceral sensory (afferent) fibers

carry information from visceral organs

motor (efferent) division

nerve fibers that carry impulses AWAY from the central nervous system organs to effector organs (muscles and glands)

somatic nervous system

consciously controls skeletal muscles (voluntary)

autonomic nervous system

automatically controls smooth, cardiac muscles, and glands

Autonomic nervous system divisions

sympathetic (stimulates) and parasympathetic (inhibits)

nervous tissue structure

neurons, support cells in CNS are grouped together as neuroglia

nervous tissue functions

support, insulate, protect neurons

astrocytes structure

abundant, star shaped cells,

Astrocytes function

brace and anchor neurons to blood capillaries, protect neurons from harmful substances in blood, control the chemical environment of the brain

microglia structure

spider-like phagocytes

microglia function

monitor health of nearby neurons, dispose of debris

Ependymal cells structure

line cavities of the brain and spinal cord

Ependymal cells function

cilia assist with circulation of cerebrospinal fluid

Oligodendrocytes (central nervous system)

wrap around nerve fibers in the central nervous system and produce myelin sheaths

PNS glial cells

schwann cells, satellite cells

schwann cells

form myelin sheath around nerve fibers in the PNS

satellite cells

protect and cushion neuron cell bodies

Neurons/nerve cells

cells specialized to transmit messages (nerve impulses)

Main regions of neurons

cell body and processes

misconception about neurons

that they touch each other, they do not, they interact

how many impulses are in a neuron

one

how many directions can an impulse go

one, from dendrites to axon

Neuron cell body

nucleus and metabolic center of the cell

neuron processes

fibers that extend from the cell body

Dendrites

conduct impulses toward cell body

axons

conduct impulses away from cell body

synaptic cleft

gap between axon terminals and the next neuron

synapse

functional junction between nerves where a nerve impulse is transmitted

myelin sheath structure

white, fatty material covering axons

myelin sheath function

protect and insulate fibers, speeds nerve impulse transmission

neuron nuclei

clusters of cell bodies in the CNS

neuron ganglia

collections of cell bodies outside the CNS in PNS

neuron tracts

bundles of nerve fibers in the CNS

white matter

collections of myelinated fibers (tracts)

Gray matter

mostly unmyelinated fibers and cell bodies

Sensory (afferent) neurons

carry impulses from the sensory recpetors to the CNS

Sensory (afferent) neurons receptors

cutaneous sense organs in skin detect pain, temp, touch, pressure

motor (efferent) neurons

carry impulses from the central nervous system to viscera and/or muscles and glands

interneurons

cell bodies located in CNS, connect sensory and motor neurons

reflexes

rapid, predictable and involuntary responses to stimuli. Occur over neural pathways called reflex arcs

reflexes types

somatic, autonomic

somatic reflexes

reflexes that stimulate skeletal muscles. Involuntary

somatic reflex example

pulling your hand away from a hot object

Autonomic reflexes

regulate the activity of smooth muscles, the heart, and glands

autonomic reflexes example

regulation of smooth muscles, heart and blood pressure, glands, digestive system

5 elements of reflex arc

sensory receptor, sensory neuron, integration center (CNS), motor neuron, effector organ

sensory receptor

reacts to a stimulus

sensory neuron

carries message to the integration center

integration center (CNS)

processes information and directs motor output

motor neuron

carries message to an effector

effector organ

muscle/gland to by stimulated

two neuron reflex arcs

simplest type

example of two neuron reflex arcs

patellar (knee jerk) reflex

three neuron reflex arcs

5 elements, receptor, sensory neuron, interneuron, motor neuron, effector

three neuron reflex arcs ex

flexor (withdrawal) reflex

brain regions

cerebral hemispheres, diencephalon, brain stem, cerebellum

main regions of cerebral hemisphere

cortex (superficial gray matter), white matter, basal nuclei (deep pockets of gray matter)

cerebral cortex (primary somatosensory area) function

receives impulses from body’s sensory receptors (except special senses)

cerebral cortex (primary somatosensory area) location

in parietal lobe posterior to central sulcus

cerebral areas involved in special senses

visual area (occipital lobe)

auditory area (temporal lobe)

olfactory area (temporal lobe)

diencephalon (interbrain) location

on top of brain stem, enclosed by cerebral hemispheres, three structures

diencephalon structures

thalamus, hypothalamus, epithalamus

diencephalon: thalamus

encloses third ventricle, relay station for sensory impulses passing upward to cerebral cortex

diencephalon: hypothalamus

regulates body temp, water balance, metabolism. houses limbic center for emotions, regulates pituitary gland, houses mammillary bodies

diencephalon: epithalamus

forms the roof of third ventricle, houses the pineal body, includes the choroid plexus(forms cerebrospinal fluid)

brain stem

provides pathway for ascending and descending tracts, provides programmed behaviors key for survival

three structures of brain stem

midbrain, pons, medulla oblongata

midbrain

extends from the mammillary bodies to the pons inferiorly, two bulging fiber tracts cerebral peduncles, convey ascending and descending impulses

pons

rounded structure just below midbrain, mostly composed of fiber tracts

medulla oblongata

merges into spinal cord, contains important center that controls heart rate, blood pressure, breathing, swallowing, vomiting

brain stem: reticular formation

diffuse mass of gray matter along brain stem, involved in motor control of visceral organs- reticular activating system (sleep cycles)

cerebrum

controls balance, provides precise timing for skeletal muscle activity and coordination of body movements

Central nervous system protectors

meninges, cerebrospinal fluid, blood-brain barrier

meninges layers

dura mater, arachnoid layer, pia mater

cerebrospinal fluid

forms watery cushion to protect brain and spinal cord

blood brain barrier

allows water, glucose, and amino acids to pass through the capillary walls, excludes potentially harmful substances from entering the brain, such as wastes

concussion

slight brain damage, typically little permanent brain damage occurs

contusion

marked nervous tissue destruction occurs, coma may occur

Death may occur after head blows due to

intracranial hemorrhage, cerebral edema

Cerebrovascular accident (stroke)

results when blood circulation to a brain area is blocked and brain tissue dies- loss of some functions or death may result

hemiplegia

one-sided paralysis

aphasia

damage to speech center in left hemisphere

transient ischemic attack

temporary restriction of blood flow to brain- numbness, temporary paralysis, impaired speech

Spinal cord function

provides a two-way conduction pathway to and from the brain

spinal cord location

extends from the foramen magnum of the skull to the first or second lumbar vertebra,

protected by vertebrae and meninges

31 pairs of spinal nerves arise from the spinal cord