Autonomic Nervous UNIT 1

Autonomic nervous system: Neurons

multipolar neurons are mainly motor neurons

pseudounipolar neurons are mainly sensory neurons

picture of the multipolar neuron, cell body is in the CNS, axon terminals to to the effector organ

picture of the pseudounipolar neuron, one axon goes to the receptor organ, the other axon goes to the cns (spinal cord), then the spinal cord sends the information to the brain.

The other type of cell in the nervous system is the neuroglia. The neuroglia has the function to support, insulate, and nourish neurons.

Neurons communicate with each other by the synapse.

Organization of the Nervous System

The central nervous system is the brain and spinal cord

knowledge gap: the peripheral nervous system is the cranial nerves and spinal nerves.

The nerves exit through the intervertebral foramen in the spinal cord.

This image shows the distribution of the organization of the nervous system.

31 pairs of spinal nerves

The spinal nerves are classified according to where they exit the spinal cord.

C8, T12, L5, S5

All of them are exiting both sets of the spinal cord in the region called the intravertebral foramen.

The cervical and lumbar regions are enlarged because they supply the upper and lower limbs.

The meninges “membranes” of the brain are the

1. dura matter

2. arachnoid matter

3. pia matter

The meninges “membranes” of the central nervous system are the

1. dura matter

2. arachnoid matter

3. pia matter

knowledge gap: the meninges covers both the spinal cord and the brain.

-Spinal nerves arise from the spinal cord gray matter

cell bodies are located in the H-shaped inner gray matter

myelinated axons constitute the outer white matter

knowledge gaps: the spinal nerves have rootlets that converge to form the anterior nerve roots and anterior nerve roots.

Spinal Nerves

Posterior/dorsal: sensory neurons or afferent neurons

Anterior/ventral: motor neurons or efferent neurons

spinal nerves are mixed nerves

“spinal nerves are mixed nerves” meaning.

1. dorsal and ventral rootlets

2. spinal nerves converge

3. spinal nerves again divide into posterior rami (to supply back muscles and skin) and anterior rami (to supply remaining anterolateral wall and limbs).

The “plexi” are the areas where the spinal nerves mix with the other nerves

Plexus Formation

Most anterior rami contribute to plexus formation for limb innervation

The posterior rami innervate the back and skin.

There is no plexus in the area of the trunk.

Plexus Formation

Plexus formation leads to the formation of multisegmental peripheral nerves.

As you can see, from a cell in the C5 region of the spinal cord, we can have the contribution to various nerves. One spinal nerve is contributing to motor fibers to many different peripheral nerves.

In this other example, we have one peripheral nerve receiving the sensory fibers from many different spinal nerves

The nervous system is divided into the a somatic nervous system and autonomic nervous system. The somatic nervous system is mainly a motor system that permits the voluntary and reflexive movements by contracting the skeletal muscle.

Somatic Fibers

GSA: general somatic afferent

GSE: general somatic efferent

Visceral Fibers

GVA: general visceral afferent

GVE: general visceral efferent

Pathway

1. touch a hot iron

2. sensory receptors in skin send signal to peripheral axon of pseudounipolar neuron

3. sensory pseudounipolar neuron cell body is in the dorsal root ganglion

remember a ganglion is a collection of neuron cell bodies outside the central nervous system.

4. heat signal reaches the spinal cord via the central axon of the pseudounipolar neuron entering via the posterior (dorsal) rootlets.

5. central axon of the pseudounipolar neuron synapses on interneuron in gray matter of the spinal cord

6. interneuron synapses on motor neuron in the ventral grey region of the spinal cord

7. axon of motor neuron exits the spinal cord through the anterior rootlets

8. anterior rootlets exit the spinal cord through the anterior rami

9. anterior rami reaches the muscle that allows the body to remove the hand from the source of the heat.

this is a reflex in this case.

There are different types of neurons in the peripheral nervous system.

Sensory neurons receive the stimuli and reach to the spinal cord

Motor neurons reach target organs

Autonomic motor neurons control movement in muscles that are not skeletal muscle (smooth muscle and cardiac muscle). It is also going to innervate glands to cause it’s contraction.

This is what was talked about in the above flashcard

Note: Autonomic motor pathways use a two-neuron chain (preganglionic and postganglionic) connected by a ganglion to amplify, distribute, and finely control signals sent to involuntary organs.

The autonomic nervous system innervates smooth muscle, cardiac muscle and glands

The autonomic efferent fibers are organized into sympathetic and parasympathetic divisions.

The cells of the sympathetic division come from the thorax and lumbar divisions of the spinal cord

The cells of the parasympathetic division come from the cranio and sacral divisions of the spinal cord

The presynaptic neuron is always located in the spinal cord

The postganglionic neuron is always located outside the spinal cord

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