Vertebrate Physiology - Ch 5

Function of the Nervous System

Acquire sensory information and generate adaptive response

What does adaptive mean in regards to the nervous system?

An appropriate response to a stimulus

What are the two forms of structural organization in the vertebrate nervous system?

Central nervous system (CNS) and peripheral nervous system (PNS)

What sets apart the CNS from the PNS?

The CNS is encased in bone, the PNS is everything else

What organs are part of the CNS?

Brain, spinal cord, retina

Why is the retina a part of the CNS?

It develops from the middle part of the brain and extends outside the skull

What organs are a part of the PNS?

Nerve fibers

What does the afferent division of the PNS do?

Carries information from the peripheria (sensors) to the CNS

What does the efferent division of the PNS do?

Transmits instructions from CNS to effector organs

Two parts of efferent division

Sematic nervous system and autonomic nervous system

What does the sematic nervous system do?

Drives motor neurons that drive skeletal muscles

Two parts of the autonomic nervous system

Sympathetic and parasympathetic nervous systems

How is information moved around the body via the nervous system?

Afferent division receives/carries division to CNS → CNS proccesses information and generates response → Efferent division carries information from CNS to effector organs

What are the three classes of neurons?

Afferent, efferent, and interneurons

What are the four parts of an afferent neuron?

1) Sensory receptor → peripheral end

2) Peripheral axon → extends from receptor to cell body

3) Cell body → dorsal root ganglion outside CNS

4) Central axon → extends from cell body into spinal cord

What are the three parts of efferent neurons?

1) Dendrites → in CNS

2) Cell body → in CNS

3) Axon → projects to effector organ

Where are interneurons found?

Within CNS

What do interneurons do?

Integrate peripheral responses to peripheral information

What do glial cells (neuroglia) do?

Maintain composition of ECF surrounding neurons;

Modulate synaptic function;

Prove myelin

What’s the most numerous type of glial cell?

Astrocytes

The processes on an astrocyte ___

Radiate out

What do the foot processes of astrocytes do?

Induce formation of blood-brain barrier → protect brain

What do astrocytes do?

Help recycle neurotransmitters and regulate contents of extracellular compostion

What do astrocytes take in and then release when recycling neurotransmitters?

Take in glutamate and send back glutamine

What do microglia do?

Conduct phagocytosis

What activates microglia to engage in phagocytosis?

Cytokines

What do ependymal cells do?

Line cavities of CNS and produce cerebral spinal fluid

What are the four types of glial cells?

Astrocytes, oligodendrocytes, microglia, and ependymal cells

What are the different glial cells derived from?

All derived from neural endoderm

What does the autonomic nervous system do?

Regulates visceral activities

Ex) Circulation, digestion, thermoregulation, pupil size

Dual innervation

Innervated by both parasympathetic and sympathetic nerve fibers

Ex) Most visceral (hollow) organs

What’s an example of the SNS found in mammals?

Sympathetic trunk lies aside spinal cord

*Sandwich filling

What’s an example of a PSNS in mammals?

Parasympathetic fibers extend from either side of spinal cord

*Bread of sandwich

What does the SNS handle?

Preparation for hard physical activity in emergenty situations

Ex) Fight or flight

What happens to the body during fight or flight?

Heart rate increases; respiratory airways open; glycogen/fat stores broken down; blood vessels that supply skeletal muscle dilate; pupils dilate

Why do respiratory airways open during fight or flight?

Increase oxygen intake → need for final electron acceptor

Why do blood vessels connecting to the skeletal muscles dilate?

Increase blood flow → more oxygen → more glucose

Why do pupils dialte during fight or flight?

Capture more light → improves distance vision

What does the PNS do?

“Housekeeping” during relaxation: digestion and emptying bladder

Automnomic pathway consists of a _____

Two-neuron chain

What are the two neurons of the autonomic pathway?

Preganglionic and posganglionic fibers

Where are preganglionic fibers in the autonomic pathway?

Extend from CNS to autonomic ganglion

→ Short

Where are postganglionic fibers in the autonomic pathway?

Innervate effector organs

→ Long

Where are sympathetic nerve fibers found?

Thoracic and lumbar spinal cord

Where are sympathetic ganglia found?

Form chain alongside spinal cord

Where are parasympathetic nerve fibers found?

Arise from cranial (brain) and sacral spinal cord

Where are parasympathetic ganglia found?

In or near effector organs

What do sympathetic and parasympathetic preganglionic fibers both release?

Acetylcholine

What do parasympathetic postganglionic fibers release?

Acetylcholine → cholinergic fibers

What do sympathetic postganglionic fibers release?

Norepinephrine (NE) → adrenergic fibers

Terminal branches of postganglionic fibers have ____ for diffuse release of neurotransmitters

Varicosities

What are the diffeent types of nervous system receptors?

Nicotinic acetylcholine, muscarinic acetylcholine, and adrenergic receptors

Where are nicotinic ACh receptors located?

On postganglionic cell bodies in autonomic ganglia

What types of channels do nicotinic ACh receptors have?

Ligand-gated nonspecific cation channels

*Depolarization: More Na+ enters than K+ leaves

Where are muscarnins ACh receptors find?

On effector cells responsive to parasympathetic system

What do the five subtypes of muscarinic Ach receptors do?

Activate second messenger systems when ACh binds → multiple effects

What does GPCR stand for?

Gene protein coupled receptors

Where are adrenergic receptors located?

On effector cells

What type of proteins are adrenergic receptors?

GPCR

What do alpha 1 receptors do?

Bind to Ne → excitatory response

What do alpha 2 receptors do?

Bind to NE → inhibitory response

What do beta 1 receptors do?

Bind equally to E (epinephrie) and NE → excitatory response

What do beta 2 receptors do?

Bind to E → inhibitory response

Where are motor neuron cell bodies located?

In ventral horn of spinal cord or in brainstem

What do axon terminals release?

ACh

What controls skeletal muscles?

Motor regions of cortex, basal nuclei, cerebullum, brainstem

*Motor neurons final common pathway

Where is the primary motor cortex?

Posterior part of frontal lobe in front of central sulcus

What does the primary motor cortex do?

Skeletal muscles move body → controls opposite side

Function of the spinal cord

Transmits information between brain/body

Integrate reflex activity between afferent and efferent divisions

What are the three regions of gray matter?

Dorsal, lateral, ventral horn

What does the dorsal horn consist of?

Cell bodies of interneurons on which afferent neurons terminate

What does the lateral horn consists of?

Cell bodies of autonomic efferent nerve fibers

What does the ventral horn consist of?

Cell bodies of somatic efferent neurons

What is white matter?

Bundle of myelinated nerve fibers (tracts)

What do the ascending tracts of white matter do?

Transmit afferent signals to brain

What do descending tracts of white matter do?

Relay messages from brain to efferent neurons

Where are spinal nerves located?

Emerge from spinal cord

What kinds of nerve fibers do spinal nerves contain?

Afferent and efferent fibers

Afferent fivers enter spinal cord through ___

Dorsal root

Efferent fibers leave spinal through ___

Ventral root

Where are cell bodies of afferent neurons clustered?

Dorsal root ganglion

Where are the neuron synapses located in respect to the stretch reflex?

Afferent, sensory neuron synapses directly on efferent, motor neuron

Motor neuron activates skeletal muscles to contract to ____

Counteract stretch

Withdrawal reflex

Withdrawal of limb from painful stimulus

What are the two ways the withdrawal relfex work?

Excited afferent neurons → stimulate excitatory interneurons → stimulate efferent motor neurons → flexor muscles (polysynaptic reflex)

Excited afferent neurons → inhibitory interneurons → inhibit efferent neurons → extensor muscles (reciprocal innervation)

Where is the somatosensory cortex located?

Anterior part of parietal lobe behind central sulcus (post-central gyrus)

What does the somatosensory cortex handle?

Initial processing and perception of somasthetic and proprioceptive sensations;

Receives sensory information from opposite side of body

Somasthetic meaning

Body surface

Proprioceptive meaning

Body position