Week 4: PNS

Question 1

Most of the information coming from afferent/sensory neurons comes in through the dorsal/alar plates. What are some exceptions?

Answer 1

Inputs from the nose (olfactory bulb) and the eyes (the diencephalon)

Question 2

What do the somatic sensory nerves detect?

Answer 2

Touch, pain, pressure, vibration, temperature, and proprioception (Special: hearing, equilibrium, vision, smell)

Question 3

What do the visceral sensory neurons detect?

Answer 3

Inside of the body: stretch, pain, temperature, chemical changes, irritation, nausea, hunger (Special: taste)

Question 4

What do the somatic and visceral motor neurons stemming from the efferent basal plate do?

Answer 4

Somatic motor (voluntary) neurons innervate the skeletal muscles

Visceral motor (involuntary) neurons innervate the smooth & cardiac muscle as well as glands–this is the ANS element of the body

Question 5

Explain the basic structure and function of elements that help the PNS and CNS interact

Answer 5

Sensory input is received from the internal/visceral(stretch, pain, hunger, nausea) andexternal/sensed(touch, sight, hearing, etc.) environments. Informationi from sensoryafferentnerves travels through thesensory gangliato theCNS, including through thecerebrum, cerebellum, brainstem,andspinal cord. This information is condensed and interpreted, either within theinterneuronsin theSCor in thebrain region of interest, and amotor response is formed in reply to the sensory input.

Question 6

What are the neural crest derivatives and how do you remember them?

Answer 6

MAGS PANE (“Max Payne”)

Melanocytes/Meninges

Adrenal medulla

Ganglia (DRG and postganglionic autonomic)

Schwann cells

Parafollicular C cells and Pharyngeal arches

Aortopulmonary septum

Nice teeth (Odontoblasts)

Endocardial cushions

Question 7

What is the interface of the PNS/CNS and how do we remember them?

Answer 7

PAD

Pia mater, the innermost layer of the meninges (connective tissue that wraps the CNS)

Arachnoid–meshlike tissue that has blood vessels between it and the pia mater

Dura mater–the tough, outermost covering layer of the CNS

Question 8

What is the function of astrocytes in the CNS?

Answer 8

Astrocytes work to support metabolic function, guidance during migration, detoxification of substances, electrical insulation and transport of blood-borne material

Question 9

What is the general structure of the peripheral nerves as it relates to layering?

Answer 9

The endoneurium is connective tissue that surrounds nerve filaments and makes up the basal lamina (correlates to pia mater)

The perineurium is connective tissue that surrounds individual fascicles (nerve bundles) (correlates to arachnoid membrane/space)

The epineurium contains a group of fascicles (correlates to dura mater)

Question 10

Describe the innervation and function of somatic nerves

Answer 10

Somatic neurons originate from the ventral horn/basal plate of the spinal cord, and exert direct control over the skeletal muscles. They are heavily myelinated to allow for very fast conduction.

Question 11

Describe the innervation and function of the sensory neurons of the body

Answer 11

The somatic and visceral sensory nerves enter the spinal cord through the dorsal root ganglia via pseudo-unipolar neurons. They synapse at the dorsal root/alar plate region of the spinal cord.

Question 12

What are the two major somatic sensory and motor types, and what is their innervation like? What do they derive from?

Answer 12

Dermatomes (sensory) are areas of the body surface (skin, etc) where all the sensory information is going into ONE DRG neuron (i.e. a region of your skin that feels cold/touch can tell you generally where that feeling is coming from)

Myotomes (motor) involve ONE motor neuron that leads to multiple muscles–this helps control the function of a certain somatic region in a synchronous manner

These derive from the somites!

Question 13

Describe myelination. Which cells myelinate nerve cells in the CNS and in the PNS?

Answer 13

Myelination occurs when oligodendrocytes in the CNS and Schwann cells in the PNS wrap layers of their cell membranes around axons. This increases the electrical conductance DOWN an axon by preventing ions from leaking out. Myelin also has a very high resistance, allowing for current to travel quickly down the axon.

Question 14

How do Schwann and oligodendrocyte cells differ in the number of axons they myelinate?

Answer 14

Schwann usually myelinate a section of a single cell, whereas oligodendrocyte cells myelinate many axons simultaneously

Question 15

What are the kinds of sensory receptors on neurons through which information is processed?

Answer 15

(1) Chemoreceptors - chemical
(2) Photoreceptors - light
(3) Thermoreceptors - heat
(4) Mechanoreceptors - stretch/pressure
(5) Nociceptors - damaging stimuli, like extreme heat, pressure, etc.

these are subdivided into the

(A) Exteroreceptors in skin

(B) Proprioceptors in muscles, tendons, and joints (muscle tension, position)

(C) Enteroreceptors in gut organs

Question 16

What are the two major kinds of general somatic efferent muscles?

Answer 16

Alpha motor neurons: large, myelinated mmotor neurons that innervate striated muscles at the NMJ

Gamma motor neurons: small motor neurons that innervate muscle spindles, control muscle stretch and muscle tone

Question 17

Where do the parasympathetic motor nerves emanate from?

Answer 17

The cranial nerves of the head and the sacral region of the spine

Question 18

Where do the sympathetic nerves emnanate from?

Answer 18

The T1-L2 vertebrae contain the region of the sympathetic ganglia/trunk/chain

Question 19

Explain the innervation of paravertebral and prevertebral ganglia

Answer 19

Information leaves the basal plate of the CNS and runs through preganglionic nerves. These synapse at the paravertebrals in the thorax, and run through the paravertebrals and synapse at the prevertebrals in the abdomen. The preganglionic nerves are cholinergic, and synapse with adrenergic postganglionic nerves, signaling at nicotinic receptors. The postganglionic nerves innervate the thorax/abdomen organs and synapse on a/B receptors on the GI tract and other relevant organs.