Chapter 12 MCQ + Essay

(b) a nerve.

(1) d

(2) b

(3) f

(4) c

(5) a

(6) a

(b) biceps muscle.

(1) SS
(2) VS
(3) VM
(4) SM
(5) VS
(6) SS
(7) SM

(b) a gland.

(b) motor neuron cell bodies.

(a) neuron cell bodies.

(c) axosomatic.

(d) the plasma membrane.

(b) neuron cell bodies in the gray matter.

(c) serial processing.

(d) axons of afferent and efferent neurons.

2, 1, 3.

Proprioception is unconscious body position sense carried ipsilaterally in the dorsal columns, lost in dorsal column lesions, and tested clinically with the Romberg sign.

Your body has sensors hidden in your muscles, tendons, and joints that are constantly tracking where every body part is — even without you looking.
This is why you can close your eyes and still touch your nose. Your brain already knows where your hand is.

Interneurons are CNS-only neurons that integrate and relay signals between sensory and motor neurons, forming the basis of complex processing, reflex arcs, and spinal cord circuitry.

Input	Interneuron	Output
Sensory neuron	Processes & integrates	Motor neuron

Sure! Here's the composition broken down the same way:

Composition:

🧠 Gray Matter:

• Neuronal cell bodies → the "headquarters" where decisions are made.

• Dendrites → receiving incoming signals.

• Synapses → where neurons actually talk to each other.

• Little to no myelin → that's why it looks gray.

White Matter:

• Myelinated axons → long cables carrying signals from A to B.

• Myelin sheath → the fatty wrapping that speeds up transmission and gives white matter its color.

• No cell bodies, no synapses → no processing happens here, just transmission.

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Location 🧠 In the Brain:

• Gray matter → on the OUTSIDE (cortex — the wrinkly surface).

• White matter → on the INSIDE (beneath the cortex).

• Exception: deep gray matter nuclei sit inside the white matter (e.g., basal ganglia, thalamus).

🧠 In the Spinal Cord:

• Gray matter → on the INSIDE (butterfly/H-shaped core).

• White matter → on the OUTSIDE (surrounding the gray).

High yield: Brain and spinal cord are opposite to each other in terms of gray/white matter arrangement!

Neuron:

• Large cell body (soma) with multiple processes

• Nissl bodies (rough ER) — for protein synthesis

• Cannot divide (post-mitotic)
  

Nucleus:

• Large, round, pale (euchromatic)

• Prominent nucleolus (large dark dot)

• Pale = actively transcribing (high metabolic activity)

Neurons vs. Neuroglia

	Neurons	Neuroglia
Structure	Large cell body, axon, dendrites, Nissl bodies	Smaller, vary by type, no axons
Function	Generate & transmit electrical signals	Support, protect, and nourish neurons
Location	Gray matter (cell bodies)	Throughout CNS & PNS
Division	Cannot divide	Can divide
Number	Less numerous	~10x more numerous than neurons

Neurons are the signal generators; neuroglia are the support crew — more numerous, able to divide, and found everywhere neurons are.

erve vs. Nerve Fiber vs. Neuron

	Neuron	Nerve Fiber	Nerve
What is it	The entire cell	Single axon + its myelin sheath	Bundle of many nerve fibers
Includes	Cell body, dendrites, axon	Axon only (+ covering)	Multiple fibers + connective tissue
Analogy	The whole wire factory	One wire	A cable containing many wires

A neuron is the whole cell; a nerve fiber is just its axon; a nerve is a bundle of many nerve fibers bound together by connective tissue.

PNS vs. CNS Nerve Damage PNS — Reversible:

• Schwann cells guide and support regrowth of damaged axons

• Schwann cells produce nerve growth factors

• Connective tissue sheaths (endoneurium) act as a scaffold for regeneration

• Axon can regrow at ~1mm/day'

CNS — Irreversible:

• Oligodendrocytes cannot guide regrowth the way Schwann cells can

• Astrocytes form a glial scar — physically blocks regrowth

• CNS produces inhibitory factors that actively stop regeneration

• No connective tissue scaffold present

PNS regenerates because Schwann cells guide regrowth along intact sheaths; CNS cannot because oligodendrocytes lack this ability and astrocytes form a glial scar that blocks regeneration.

Axon:

• Single process that carries signals away from the cell body (efferent)

• Can be myelinated or unmyelinated

• Ends in axon terminals (synaptic knobs) that release neurotransmitters

Dendrite:

• Multiple branching processes that carry signals toward the cell body (afferent)

• Usually short and unmyelinated

• Greatly increase the surface area for receiving signals

Dendrites bring signals in; axons send signals out.

They sit in the middle one end touching the periphery, one end reaching into the spinal cord so the signal goes straight through with no detours.

Myelinated

• One Schwann cell wraps around one axon — many times — forming a thick myelin sheath.

• Creates nodes of Ranvier (gaps between Schwann cells) where the signal jumps.

• Conduction is saltatory (fast) — signal leaps node to node.

• Found in fibers requiring speed (motor, proprioception, touch).

Nonmyelinated

• One Schwann cell loosely envelops multiple axons simultaneously — just tucking them into its surface, no wrapping.

• No nodes of Ranvier.

• Conduction is slow and continuous.

• Found in fibers carrying pain and temperature (C fibers).

In myelinated fibers, one Schwann cell wraps one axon many times for fast saltatory conduction; in nonmyelinated fibers, one Schwann cell loosely cradles many axons with no wrapping, resulting in slow continuous conduction