2Psy Neuro ZELF 8.

Peripheral nervous system

Nerves

=in PNS: large bundles of axons separated by connective tissue

1. Cell bodies & dendrites of neurons are located in CNS or in ganglia (clusters of cell bodies outside CNS)

2. Axons from CNS together form the spinal cord

 

 =>thus: nerve≠neuron!!
 ->nerve fiber=axon

 ->nerve=bundles of axons

Human nerves

1. Cranial nerves
2. Spinal nerves

Cranial nerves

=12 pairs (originating from the brain)

 ->motor, sensory, or both (in which case they operate bidirectionally).

 ->mostly connected to head/neck (except for cranial nerve XI (neck and back muscles) and cranial nerve X)

 ->zie knowt lijst vorig jaar

Vagus nerve X

=special case!

1. Connected not only to pharynx & larynx but also to most internal organs

 2. Originates from medulla oblongata (which communicates with the hypothalamus)

 =>plays crucial role in homeostasis, fight-or-flight response…

Spinal nerves

=originating from spinal cord (each pair serves specific body region)

1) Roots/wortels separate axons of sensory (dorsal) & motor neurons (ventral).

 ->soma of sensory neurons located in dorsal root ganglia (also 31 pairs of dorsal roots)

 ->soma of motor neurons located in spinal cord.

 

2) The two roots eventually merge after exiting spinal cord, forming a mixed nerve

Spinal Cord Organization

1. Dorsal horns contain interneurons
2. Ventral horns contain dendrites & cell bodies of motor neurons

Somatic NS

1. Nerves in here: serve skin, skeletal muscles & tendons
2. NT=acetylcholine
3. One neuron per impulse: most cranial & spinal nerves

Reflexes

~not all somatic motor responses are voluntary (some automatic)

Example: hand touches a glass

  → sensory fibers in nerve bundle transmit to dorsal root ganglion

 → to dendrites of interneurons in dorsal horn, then to brain (pain perception)

→ interneurons transmit to dendrites of motor neurons in ventral horn

→ long axon fibers in spinal nerve carry impulse to effector cells (e.g., muscles)

ANS (autonoom ZS)

=autonomic nervous system

~regulates activity of cardiac & smooth muscles, organs & glands

 ->divided into sympathetic & parasympathetic nervous systems

 (which generally have opposite effects on target organs)

Common features of ANS

1) Automatic & involuntary

 ->ANS functions without conscious control

2) Affects same organs with opposite effects

 ->influence same organs in opposite ways to maintain balance

 

3) Utilizes 2 neurons & 1 ganglion per impulse

 1. Neuron 1: cell body in CNS: sends preganglionic fiber to the ganglion

 2. Ganglion: acts as a relay station

 3. Neuron 2: cell body in ganglion: sends postganglionic fiber to target cell

 

4) Important role in homeostasis (adapts body responses based on internal & external conditions)

1. Sympathetic NS

1) Origin: primarily from thoracolumbar region of spinal cord (mid-spine, midden)

 

2) Structure: short preganglionic & long postganglionic fibers

 

3) Function: fight-or-flight response (preparing body for high-stress situations)

 

4) NT: norepinephrine

2. Parasympathetic NS

1) Origin: from certain cranial nerves (including vagus nerve) & sacral region of spinal cord (lower spine)

 ~also known as craniosacral

 

2) Structure: Long preganglionic fibers and short postganglionic fibers (ganglia often near or within the target organ)

3) Function: "Rest-and-digest" response (promoting relaxation & recovery)

 

4) NT: Acetylcholine