A&P Unit 3 (CH 7+8)

Functions of the Nervous system

Sensory input. integration, motor output

Integration

processes/interprets sensory input, decides what should be done at each moment

Motor Output

activates effector organs to cause a response

PNS

Cranial nerves, spinal nerves, peripheral nerves, ganglia, carries sensory input to the CNS and motor output away from it

Somatic motor

Motor fibers to skeletal muscle, voluntary control

PNS 2 divisions

Sensory and motor

Motor division

Somatic NS and autonomic NS, carries impulses away from the CNS

Neurons

Respond to stimuli, transmit electrical signals, are amitotic, have a high metabolic rate, have a cell body and one or more slender processes

Astrocyte

CNS, regulate the chemical environment, interact with capillaries and neurons, guide young neurons, and help form synapses

Microglial cel

CNS, monitors neuron health, becomes phagocytic after injury or infection

Ependymal cell

CNS, lines ventricles and central canal, cilia help move CSF, participates in the choroid plexus

Oligodendrocyte

CNS, forms myelin segments around portions of multiple axons

Satellite cell

PNS, surrounds neuron cell bodies in ganglia, regulates their local enviornment

Schwann cell

Form myelin sheaths around axons in the PNS, important for peripheral nerve regeneration

Perikaryon/soma

neuron cell body, major metabolic center, has pigment inclusions

Ganglia

collection of nerve cell bodies in PNS

Nuclei

cluster of nerve cell bodies in the CNS

Dendrites

Receive incoming messages and carry them toward the cell body, produce graded potentials, not myelinated

Axon hillock

Trigger region where a sufficiently strong graded potential initiates an action potential.

Axon

Conducts action potentials away from the soma, one axon per neuron, long axons are nerve fibers

Axon terminals

Knob-like endings of axons with neurotransmitter vesicles

Synaptic cleft

gap between a presynaptic axon terminal and the next cell, entire functional junction.

Sensory neuron

transmit impulses from sensory receptors in the skin/internal organs toward CNS, unipolar

Motor (efferent) neuron

carry impulses away from the CNS to the effector organs, multipolar

Interneurons neuron

association neuron, make up 99% of neurons, multipolar, pyramidal cells

Tracts

bundles of nerve fibers in the CNS

White matter

Collections of myelinated fibers/tracts, fatty myelin gives color, deep in cerebral cortex

Gray matter

mostly unmyelinated fibers and cell bodies

Myelin

Lipid-rich protien, insulates axons, increases conduction speed, action potential is regenerated at the node, myelinated fibers conduct faster than unmyelinated fibers, CNS axons regenerate poorly, schwann cells important to the more successful regeneration that can occur in the PNS.

Myelination in PNS

Formed by Schwann cells, cytoplasm of Schwann cell squeezed between membrane, plasma membrane of myelinating cells has less protein than most cells, channel/carrier proteins absent

Myelination in CNS

Formed by Oligodendrocytes, more than one segment/flat processes that can coil around multiple axons, lack outer collar of perinuclear cytoplasm b/c cell extensions do the coiling

Resting membrane potential

At rest the membrane polarized, inside is negative, more permeable to K+ than to Na+ because of K+ leak channels.

sodium-potassium pump

uses ATP to maintain gradients by moving 3 Na+ out and 2 K+ in, restores/maintains ion gradients, does not directly create each action potential.

Na and K+ concentration in a resting membrane

Na+ concentration is higher outside, K+ concentration is higher inside

How does action potential spread?

If enough sodium enters the cell, the action potential starts and spreads over the entire axon, fibers with myelin sheaths conduct nerve impulses more quickly

Repolarization

Na+ channels inactivate, membrane impermeable to Na+, voltage-gated K+ channels open, K+ leaves to repolarize membrane, sodium-potassium pump restores Na+ and K+ ions, 3 Na+ ejected from cell, 2 K+ return to cell

Repolarization

membrane returns toward its negative resting state

Action potential sequence

Stimulus and graded potential, threshold reached, depolarization, repolarization, hyperpolarization/refractory period, gradient maintenance

Stimulus and graded potential

A stimulus opens gated channels, allow Na+ to enter locally, local depolarization occurs, magnitude varies with stimulus strength.

Threshold

Depolarization at the trigger zone reaches threshold, all-or-none action potential begins.

Depolarization

Voltage-gated Na+ channels open, Na+ rushes into the axon, membrane potential becomes less negative and briefly positive,

Repolarization

Na+ channels inactivate, voltage-gated K+ channels open, K+ leaves, inside becomes negative

Hyperpolarization and refractory period

K+ channels close slowly, membrane briefly becomes more negative than resting, limits immediate re-firing and helps enforce one-way propagation

Gradient maintenance

Leak channels, Na+/K+ pump maintain, restore ion distributions, the neuron returns to stable resting conditions

Transmission at The Synapse steps

Action potential reaches the presynaptic axon terminal, depolarization opens voltage-gated Ca2+ channels, Ca2+ enters/triggers synaptic vesicles to fuse with presynaptic membrane, neurotransmitter released by exocytosis/diffuses across the synaptic cleft, binds to receptor on postsynaptic membrane, receptor activation produces a graded postsynaptic potential, neurotransmitter action ends through reuptake, enzymatic breakdown, or diffusion.

What if Voltage-gated Ca2+ channels are blocked?

Vesicles do not fuse normally, so neurotransmitter release falls or stops.

What if the postsynaptic receptor is blocked?

The transmitter may be present, but the postsynaptic cell cannot respond normally.

What if reuptake transporter is blocked?

Neurotransmitter remains in the cleft longer, prolonging or strengthening receptor activation.

What if Axon propagation is blocked

Signal lasts longer because transmitter breakdown is slowed.

What if neurotransmitter-degrading enzyme is blocked?

Signal lasts longer because transmitter breakdown is slowed.

Somatic reflexes

Reflexes that stimulate the skeletal muscles, involuntary

Autonomic reflexes

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

Basic arc of a reflex

receptor, sensory neuron, integration center, motor neuron, effector

Multiple sclerosis

Damage to myelin around nerve fibers, fiber exposed, signal can’t travel smoothly, leads to weakness, visual problems, paresthesia, fatigue, and balance trouble

Neural Tube

embryonic structure that the brain and spinal cord originate from

Primary Brain Vesicles

forebrain, midbrain, hindbrain, rest of neural tube developed into the spinal cord

Secondary Brain Vesicles

Form from primary vesicles, telecephalon, diencephalon, mesencephalon, metencephalon, myelencephalon

What does telecephalon turn into?

cerebrum, cortex, white matter, grey matter

What does diencephalon turn into?

thalamus, hypothalamus, epithalamus, retina

What does mesencephalon turn into?

brain stem, pons

What does metencephalon turn into?

brain stem, pons, cerebellum

What does myelencephalon turn into?

Brain stem, medulla, oblongata, spinal cord

Cerebrum

Higher thought and voluntary movement, two hemispheres, outer cortex of gray matter, inner white matter, balance, fibers connect sides

Cerebral hemispheres

Paired parts of the brain, more than half the brain mass, surface made of ridges/grooves, cortex (superficial gray matter), white matter, basal nuclie (deep pockets of gray matter)

Corpus callosum

Connects the two cerebral hemispheres

Primary somatosensory

receive sensory info from body and proprioceptors, in the postcentral gyrus of the parietal lobe

Somatosensory association

Integrates sensory information, helps identify an object's size, texture, and relationships between its parts

Visual sensory area

extreme posterior tip of the occipital lobe, largest cortical sensory area, receives feedback from retina of the eye, visual space on the opposite side of the body is mapped

Auditory-primary

surrounds the primary visual cortex, covers much of the occipital lobe, sound energy exciting the hearing receptors of the inner ear, interpreted as pitch, loudness, and location

Vestibular

part of the cortex responsible for conscious awareness of balance

Olfactory

medial aspect of the temporal lobe in a small region called the piriform lobe, conscious awareness of different odors

Gustatory

perceiving taste stimuli, \located in the insula just deep to the temporal lobe

Auditory-association

permits the perception of the sound stimulus, memories of sounds heard in the past appear to be stored here, wernicke’s area

Visceral sensory

posterior to the gustatory cortex, conscious perception of visceral sensations (upset stomach, full bladder, etc)

Prefrontal cortex function

Planning, judgment, personality, working memory, executive functions

What happens if prefrontal cortex is damaged

Changes in judgment, inhibition, or personality

Broca area

Speech production, left hemisphere, person knows what they want to say but is unable to produce the words or sentence

What if Broca’s area is damaged?

Knows what to say but has difficulty producing words

Visual Area

Receives feedback from retina of the eye, visual space on the opposite side of the body is mapped

Primary motor area

Allows us to consciously move skeletal muscles, motor neurons from pyramidal

Olfactory Area

Conscious awareness of different odors.

Basal nuclei

Help regulate movement and suppress unwanted movement, pockets of grey matter

Wernicke area

Language comprehension, fluent but nonsensical speech, impaired understanding

Multimodal Association Areas

receive inputs from multiple senses, send outputs to multiple areas, allows us to give meaning to the information that we receive, store it in memory, tie it to previous experience and knowledge, and decide what action to take

Posterior Association Area

Recognizes patterns and faces, helps with spatial awareness, combines sensory information, and helps understand language, binds different sensory inputs into a coherent awareness of entire scene unfolding

Prefrontal Cortex

in frontal lobe, working memory, intellect, still developing

Limbic Association Area

Gives experiences emotional significance and helps form memories, includes gyrus, hippocampus, hippocampus establish memories

Thalamus

Major relay for sensory information to the cerebral cortex, participates in motor relay and memory, large number of nuclei

Hypothalamus

Major homeostatic and visceral control center (body temp, hunger/thirst, sleep-wake cycles, autonomic regulation, emotional responses, and endocrine control), produce ADH and oxytocin.

Epithalamus

forms the roof of the third ventricle, pineal gland secretes the hormone melatonin, helps regulate the sleep-wake cycle

Limbic system

Emotion, motivation, and memory processing, amygdaloid body is critical for responding to perceived threats

Midbrain

Visual and auditory reflex centers, motor pathways, nuclei for CN III and IV.

Pons

Bridge/relay to cerebellum, helps regulate respiratory rate and depth, nuclei for CN V-VII.

Medulla oblongata

Conduction pathway between higher centers and spinal cord, centers for heart rate, vessel diameter/respiration/swallowing, nuclei for CN VIII-XII

Reticular formation/RAS

Maintains cortical alertness, filters repetitive stimuli, and helps regulate motor and visceral activity

Cerebellum

Compares motor plans with sensory feedback to produce smooth coordinated movement, balance and posture