The Human Nervous System

nervous system

• functions: collects, processes, responds (to stimuli

• systems

  • peripheral: sense, motor (stimulate for a reaction)

    • nerves: bucle of axons

      • cranial nerves

      • spinal nerves

    • ganglia: clusters of cell bodies

  • central: integrate, process, coordinate

    • brain

    • spinal

neuroglial cells

• functions

  • fill spaces

  • structural framework

  • produces myelin

  • phagocytes

  • able to divide

• central Nervous system (CNS)

  • microglial cells

    • defend & recycle debris

  • oligodendrocytes

    • provide myelin sheath

  • astrocytes

    • structure, transport between blood vessels & neurons, regulate ions & nutrients, scar tissue after damage in CNS

  • Ependymal cells

    • membranes covering spinal cord, linings in brain

• peripheral nervous system

  • satellite cells

    • protect cell bodies

  • schwann cells

    • myelin sheath around axons

  • myelination is incomplete in infancy

    • increases with age & development

the neuron

• structure

  • cellbody

    • nissl bodies - RER

  • dendrites

  • axon

    • telodendria

    • axon terminals

    • myelin sheath = faster impulse speed (up to 100x)

  • nodes of ranvier

• structural classification

  • multipolar neuron

  • unipolar neuron - rare eg. eye retina

  • bipolar neruon

• functional classifications

  • sensory: mostly unipolar

  • motor: mostly multipolar

  • acronym SAME

    • sensory

    • afferent

    • motor

    • efferent

nerve impulses

• synapse

  • synaptic cleft

  • synaptic vesicles

  • neurotransmitters

• presynaptic vs postsynaptic

  • glands

  • muscles

  • neurons

• threshold

nerve impulses

• resting potential

  • polarized

  • slightly negative

  • Na-K pump & diffusion

  • voltage = -70mV

  • plasma membrane more permeable to K+ then Na+

    • more K+ leak channels than Na+ leak channels

    • thus more positive charges leave than enter

  • negatively charged protiens remain inside

• depolarization to threshold potential

  • approximately -55mV

  • all or nothing event

  • graded potential vs Action potential

  • Na ion channels openn

  • channel proteins:

    • voltage gated

    • ligand gated

    • echanically gated

• moving impuse/action potential

  • Na ion channels ipen

  • impulse passes

  • K ion channel open

  • release of neurotransmitters

• undershoot & return to resting potential

  • voltage gated K+ gates close around -70mV

    • dont all close at once

    • can be breif period of hyperpolarziation

  • sodium-potassium pump firn tunes the results & re-establishes the resting potential

clinical note

• novocain is an anesthetic used primarily by dentists, works by closing the gates of ion channels in the membranes of nnerve cells = no depolarization to threshold

continuous

• unmyelinatyted aons

• slower speed - 0.5-2.0 msec

• eg. sensory neurons for pain

saltatory

• action potential “skips” between nodes of ranvier

• myelinated axxons

• much faster - 100 m/sec

• eg motor neurons

synaps

• neurtotransmitters

  • chemical messengers

    • packaged in vesicles & leave axon terminal by exocytosis

    • diffuse across the synaptic cleft (space) to stimulate the next cell

  • excitatory

    • depolarization effect

  • inhibitory

    • hyperpolarization effect

clinical connection

• snake venom causes paralysis by either preventing the release of neurtransmitters or by blocking the receptoors on the next cell

meninges (CNS)

• layered membranes

• dura mater

  • outermost layer, fibrous, connective tissue

  • lots of blood vessles & nerves

  • lines inside of skulls (periosteum)

  • can extend inward to divide brain lobes etc

• arachnoid mater

  • thin & weblike, no blood vessles

  • subarachnoid space

    • cerebrospinal fluid (CSF) - important in protection & nutrition

• pia mater

  • lines brain & spinal cord

  • lots of nerves & blood vessles to nourish

spinal cord structure

• cervical enlargement - nerves to upper limbs

• lumbar enlargement - nerves to lower limbs

• anterior horns - motor fibers

• posterior horns - sensory fibers

• central canal continues CSF

spinal cord functions

• ascending tracts - sensory to brain

• descending tracts - brain motor impulses to muscles & glands

• spinal reeflexes

nerve pathways

• reflex arcs

  • sensory (afferent) neuron → interneurons (in CNS) → motor (efferent) neurons

• reflexes

  • autonomic responses

  • patellar reflex

    • patella tendon → stretch quadriceps femoris → sensory neruon → spinal cord → motor neruon → quadriceps femoris

  • withdrawal reflex

brain

• 4 major portions

  • cerebrum

    • largest

    • sensory/motor functions

    • higher order mental functioning

    • right & left cerebral hemispheres

    • connected - corpus callosum

    • sepereated - dura mater

    • cerebral cortex

      • ridges = gyro

      • shallow folds = sulcus

        • divide hemispheres into lobes

      • deep grooves = fissures

        • longitudinal - sperarate hemispheres

        • horizontal - sepereates cerebellum

      • outermost portion of cerebrum

      • contains 75% of all neuron cell bodies in nervous system

      • under layer is white matter

  • diencephalon

  • brainstem

  • cerebeullum

• lobes of brain

  • central sulcus

    • frontal lobe - motor control & abstract intellect

    • perietal lobe - sensory perception & interpretation

  • lateral sulcus

    • temporallobe - hearing, smell

  • parieto-occippital lobe - vision

• areas of the brain

  • wernicke’s area

    • sensory speech

      • need for hearing & seeing to interpret language

    • usually on left hemisphere

  • broca’s area

    • motor speech

      • need for moves muscles necessary for speech

    • usually on left hemisphere

• basal ganglia

  • specialize in:

    • processing information on movement

    • executing well-practiced habitual actions

    • learning new actions in novel situations

  • parkinson’s disease

• 4 functional areas of the cerebral cortex

  • motor'

    • Primary motor – voluntary body

    • Premotor - complex

    • Broca’s

  • Sensory

    • primary somatosensory cortex

    • occipital lobe

    • temporal lobe

  • association

  • integration - all lobes

    • wernickes

    • prefrontal

• ventricles & CSF

  • ventricles = cavities of the brain that are filled with cerebrospinal fluid

  • spinal tap to asses pressure in spine

  • dienephalon

    • processes sensory information

      • thalamus

        • sensory relay

      • hypothalamus

        • hunger/thirst

        • body temp

        • hormone secretion

      • pituitary glands

        • more homeostasis

      • pineal glands

        • sleep

limbic system

• involved in many emotions & motivations, particularily survival related ones

• involved in emory

  • amygdala

    • memories are stored & where

  • hyppocampus

    • sends memories out to cerebral hemisphere for long term storage

    • retrieces them when necessary

brainstem

• connects parts of the nervous system

• regulates some visceral activities

• midbrain

  • visual & auditory reflex movement

  • subconsious body movement

• pons

  • connects cerebrum to most outer parts of the brian

  • coordinate movement on each side of the body

• medulla oblongata

  • autonomic

  • functions (heaert rate, breathing & blood pressure)

  • somecoordination

• reticular formation

  • sleep/wake cycles

  • net work of nerve fibers

  • filters out background stimuli

cerebellum

• coordinates voluntary muscular movements, posture, balance

• connects to CNS via nerve tracts called peduncles

peripheral nervous sysste (PNS)

• nerves that branch off from CNS to connect to body

• cranial nerves

  • twelve pairs of nerves originate in the brian stem

    • I - Olfactory - sensory - smell

    • II - Optic - sensory - vision

    • III - Oculomotor - motor - most eye movement

    • VII - facial - both - facial expression, taste

    • X - vagus - both - speech, gag reflex, parasympathetic

• spinal nerve

  • 31 pairs of nerves

  • each nerve is named for the vertebra above it

  • plexus - spinal nerves combining on way to peripheral body part

• autonomic - no need to think about it

  • motor neurons that control smooth muscles

  • no consious thought

  • sympathetic

    • flight or fight

    • thoracolumbar

    • ganglia are close to the spinal cord

  • parasympathetic

    • functions for resting, digesting, repair

    • craniasacral

    • ganglia are found closer to the organ, gland, or muscle being affected

  • preganglionis fibers vs postganglionis fibers

• somatic nervous system

  • consious

  • connect to skin & skeletal muscles