BIO115 chp.14

Satellite cells

• Arranged around neuron cell bodies in ganglia

• Electrically insulates PNS cell bodies

• Regulates nutrient and waste exchange

Neurolemmocytes (Schwann cells)

Wrap around axons within the PNS

Myelinates and insulates PNS axons

Ganglia

Cluster of neuron cell bodies

Nerves:

Bundles of axons, connective tissue layers and blood vessels

Cranial nerves

extend from the brain

Spinal nerves

extend from the spinal cord

Sensory nerves

Contain only afferant neurons that relay information toward the CNS

Motor nerves

Contain only efferent neurons that relay information from the CNS

Mixed nerves

contain both sensory and motor neurons

Afferent Somatic peripheral nervous system

Comes from the skin and muscles. Includes touch, pain pressure, temperature, and proprioception

Afferent Visceral PNS

Comes from within the body, includes stretch, pain, temperature, hunger, and taste

Efferent Somatic PNS

Sends signals from the central nervous system to skeletal muscles, enabling voluntary movement.

Efferent visceral PNS

Involuntary, automatic. Innervation of smooth muscle, cardiac muscle, glands, Also known as the autonomic nervous system

Root

Formed by merged rootlets that branch off from the spinal cord

Anterior roots contain

motor axons only

Posterior roots contain

sensory axons only

Spinal nerve

Where each anterior root and its corresponding posterior root merge with the intervertebral foramen

Spinal nerve:

where each anterior root and it’s corresponding posterior root merge within the intervertebral foreamen

Spinal nerve contains

both motor and sensory axons

Posterior rami

Innervate the deep muscles and the skin of the back

Anterior Rami

Innervate the anterior and lateral portions of the trunk and upper and lower limbs

Dermatome

segment of skin innervated by a single spinal nerve

Nerve plexus

a network of interweaving anterior rami of spinal nerves

Left and right cervical plexuses are formed by the

anterior rami of spinal nerves c1-c4

Brachial plexus are formed by

Formed by anterior rami of c5-t1

Branches brachial plexuses innervate

the pectoral girdle and the entire upper limb of one side of the body

Lumbar plexus is formed by

Anterior rami of spinal nerves L1-L4

Branches of the lumbar plexus innervate

The hip, thigh, and leg

Sacral plexus is formed by

is formed by the anterior rami of spinal nerves L4-S4.

Branches of the sacral plexuses innervate

The gluteal region, pelvis, perineum, posterior thigh, and most of the leg and foot

Reflexes

rapid, automatic, involuntary reactions of muscles or glands to a stimulus

somatic reflexes

involve the contraction of skeletal muscles in response to stimuli, enabling quick reactions to certain stimuli.

Visceral reflexes

involve the contraction of smooth and cardiac muscles or glandular secretion in response to stimuli, often regulating involuntary functions such as heart rate and digestion.

Reflex arc

Neural pathway involved in accomplishing reflex activity:

• Receptor

• Sensory neuron

• integration center

• Motor neuron

• effector

Monosynaptic reflex

the simplest reflex, sensory axons, synapes directly on the motor neurons which then project to the effector to produce a rapid response.

Polysynaptic reflex

Have more complex neural pathways and have several synapses involving interneurons

Hypoactive reflex

A reduced or absent reflex response due to lower activity of the reflex arc components.

Hyperactive reflex

An exaggerated or overly brisk reflex response caused by increased activity of the reflex arc components.

Spinal cord

vital linkbetween the brain and the rest of the body

• Extends from the foramen magnum to the L1 vertebra

• Approximately 16-18 inches long and half the diameter of a pinky finger (3/4 of an inch

One important function of the spinal cord and spinal nerves

Structural and functional link between the brain and the rest of the body

Another important function of the spinal cord and spinal nerves

Spinal reflexes

Conus medullaris

Located around the L1 vertebrae, marks the official end of the spinal cord proper

Cauda equina

a group of axons that extend inferiorly from the conus medullaris

Filum terminale

Thin strand of pia mater that attaches the conus medularis to the coccyx

Epidural space

The outermost protective layer of the dura meninge surrounding the brain and spinal cord, providing a tough barrier against injury.

Subdural space

The cavity between the dura mater and the arachnoid mater that contains a small amount of fluid.

Subarachnoid space

The area between the arachnoid mater and pia mater that contains cerebrospinal fluid, providing cushioning and support to the brain and spinal cord.

Denticulate ligaments

Fibrous extensions of the pia mater that anchor the spinal cord to the dura mater, providing stability.

Subdural space

The area between the dura mater and the arachnoid mater that holds a small amount of cerebrospinal fluid, serving as a protective cushion.

Gray matter

contains dendrites and cell bodies of neurons, unmyelinated axons

White matter

made up of myelinated axons

Gray matter in spinal cord

centrally located in the spinal cord, sectioned shape resembles a butterfly. Sectioned into regions called horns

Anterior horns

house the cell

Posterior horns

contains the axons of sensory neurons and the cell bodies of interneurons

Lateral horns

Only found in the T1-L2 portion of the spinal cord. Contains the cell bodies of autonomic motor neurons

Gray commissure

A bar of gray matter connecting left and right sides of the spinal cord that mostly contains unmyelinated axons

Funiculi

White matter in the spinal cord partitioned into three columns: posterior, lateral, and ventral.

Posterior funiculi

Contains sensory (ascending) tracts

Lateral funiculi

Contains sensory (ascending) and motor (descending) tracts

Anterior funiculi

Contains sensory (ascending) and motor (descending) tracts, connected by white commissure

Tract

A group of myelinated axons that have a common origin, a common destination, and a similar function

Name of each reflects its origin and destination

Conduction pathway

sequence of two or more neurons that connects the CNS to the PNS, each pathway includes components that are withing the brain, spinal cord, and peripheral nerves

Sensory pathways

Ascending pathway that relay sensory information from sensory receptors to the brain

Primary neuron (sensory)

receptor to spinal cord

Secondary neuron (sensory)

spinal cord to thalamus

Tertiary neuron

thalamus to cerebral cortex

Motor pathways

Descending pathways that relay motor output from the brain to eff

Upper motor neuron

neurons that originate in the motor cortex and project down to lower motor neurons.

Lower motor neuron

neurons that directly innervate skeletal muscles, transmitting signals from the spinal cord to the muscles.

Preganglionic fiber

The first motor neuron in the autonomic system synapse within the lateral horn of the spinal cord, where it exits the anterior root and joins in the spinal nerve, myelinated

Postganglionic fiber

the second motor neuron in the autonomic system that extends from the ganglion to the target effector, such as smooth muscle or glands. Unmeylinated.

Sympathetic ANS

Dominates in emergency or stressful situations. Promotes responses that prepare the body for strenuous physical activity

Parasympathetic ANS

Dominates in a quiet, relaxed situations. Promotes body maintenance activities like digestion.

Central nervous system origins for the sympathetic ANS

Thoracic and lumbar

Central nervous system origins for the parasympathetic ANS

Cranial and sacral

Preganglionic fiber length in the sympathetic ANS

short

Preganglionic fiber length in the parasympathetic ANS

long

Postganglionic fiber length in the sympathetic ANS

Long

Postganglionic fiber length in the parasympathetic ANS

short

Divergence ratio in the sympathetic ANS

1:20

Divergence ratio in the parasympathetic ANS

1:4

Neurotransmitter released by neurons in the ANS

Acetylcholine (ACh) and Norepinephrine 

What does acetylcholine do

a neurotransmitter that enables communication between nerve cells and muscles, primarily facilitating muscle contraction and parasympathetic responses in the autonomic nervous system.

What does norepinephrine do?

a neurotransmitter involved in the sympathetic nervous system that increases heart rate, blood pressure, and energy availability during stress.

ANS receptors

Cholinergic receptors

Adrenergic receptors

Cholinergic receptors

are a type of receptor that responds to the neurotransmitter acetylcholine and are involved in both the central and peripheral nervous systems.

Adrenergic receptors

are a type of receptor that responds to the neurotransmitters norepinephrine and epinephrine, playing a crucial role in the sympathetic nervous system by mediating responses such as increased heart rate and blood pressure.

Nicotinic receptors

a cholinergic receptor that bonds to ACh, found on postganglionic cell bodies

Muscarinic receptors

a type of cholinergic receptor that binds to ACh, named for a mushroom poision, and mimics the ACh effects. Found on effector cell membranes

The postganglionic neurotransmitter for the sympathetic nervous system is 

norepinephrine

Postganglionic neurotransmitter

acetacoline

Sympathetic stimulation

• Increases heart rate

• Constricts blood vessels

• Dilates the bronchioles

• Decreases motility, inhibits digestive secretions

• Relaxes bladder (filling)

• Glucose is released

• Fatty acids are released

Parasympathetic stimulation

• Decreases heart rate 

• constricts the bronchioles 

• increases motility, stimulates digestive secretions

• Constricts bladder (emptying)

• Constricts the pupil

• Does not release glucose or fatty acids