A&p Lecture 8. Nerve Pathways

Front 1

lobes of the brain

Back 1

- frontal lobe
- occipital lobe
- parietal lobe
- temporal lobe

Front 2

sulcus

Back 2

or sulci (pl.) - shallow grooves in the surface of the brain, that divide each hemisphere into lobes

it surrounds the gyri

Front 3

gyrus

Back 3

ridge on the cerebral cortex;

it is generally surrounded by one or more sulci

Front 4

What is located in the postcentral gyrus?

Back 4

PRIMARY SENSORY CORTEX

the main sensory receptive area for the sense of touch

Front 5

What is located in the precentral gyrus?

Back 5

PRIMARY MOTOR CORTEX

It controls movements of specific body parts.

The precentral gyrus is in front of the postcentral gyrus from which it is separated by the central sulcus.

Front 6

What lobe of the brain contains the primary motor cortex?

Back 6

FRONTAL LOBE

Front 7

What lobe of the brain contains the primary sensory cortex?

Back 7

PARIETAL LOBE

Front 8

regions of the brain stem

Back 8

- midbrain
- pons
- medulla oblongata
- reticular formation

Front 9

The medulla oblongata becomes what structure when it exits the cranial cavity?

Back 9

spinal cord

Front 10

What is white matter?

Back 10

- component of the CNS
- contains myelinated axons, that run together in bundles called tracts (ascending and descending)

- tracts function as the "highways" along which sensory input travels to the brain and motor output travels from the brain to skeletal muscles and other effectors.

Front 11

What is gray matter?

Back 11

- component of the CNS
- contains dendrites and cell bodies, and short nonmyelinated axons
- portions of sensory neurons and motor neurons found in grey matter

- function of grey matter is to route sensory or motor stimulus to interneurons of the CNS in order to create a response to the stimulus through chemical synapse activity. Grey matter structures (cortex, deep nuclei) process information originating in the sensory organs or in other grey matter regions. This information is conveyed via long axons, which form the bulk of the cerebral, cerebellar, and spinal white matter.

Front 12

What is a synonym for anterior?

Back 12

VENTRAL

Front 13

What is a synonym for posterior?

Back 13

DORSAL

Front 14

What is contained in the DORSAL HORN?

Back 14

collection of 2nd order sensory cell bodies, and axons of interneurons as well as axons of incoming sensory neurons

Front 15

What is contained in the VENTRAL HORN?

Back 15

collection of cell bodies of lower motor neurons (LMN)

Front 16

What forms a spinal nerve?

Back 16

Within the spinal canal the anterior and posterior roots unite to form a mixed spinal nerve.

Front 17

What cell bodies are contained in the dorsal root ganglion?

Back 17

cell bodies of first order (primary) afferent or sensory neurons. No synapses occur here!

Front 18

What are the branches of the spinal nerve?

Back 18

- dorsal ramus
- ventral ramus
- meningeal branch
- rami communicantes

Front 19

What is a dermatome?

Back 19

Area of skin that provides sensory input to the CNS via the posterior roots of one pair of spinal nerves or via the trigeminal (V) nerve.

Front 20

What goes out of the ventral root?

Back 20

nerve impulses from the CNS

Front 21

What comes into the dorsal root?

Back 21

nerve impulses from sensory receptors in the skin, muscles, and internal organs into the CNS. Dorsal root contains only sensory axons.

Front 22

A ventral branch of the root contains what type of fiber?

Back 22

motor

Front 23

How many neurons are in sensory and motor chains?

Back 23

SENSORY CHAINS - 3 neurons. The sensory receptor receives the signal, and passes the signal down a chain of three neurons that ends at the sensation-specific cortical region. The thalamus is the relay station for all sensory info going to the cortex. It contains cell bodies of all the 3rd order sensory neurons.

MOTOR CHAINS - 2 neurons.
The cortical region communicates to the end muscle via a chain of two neurons. The 2nd (lower) motor neuron plus the NMJ constitute the motor unit. The ventral horn contains the cell bodies of lower motor neurons.
Thus, there are no synapses between ventral horn and NMJ.

Front 24

What is the lateral horn?

Back 24

collection of cell bodies of preganglionic sympathetic fibers. These are efferent myelinated fibers and will pass out of the spinal cord through the ventral root. Lateral horn is only located in the spinal cord between the levels of T1-L2 (L3): thoracic and upper lumbar segments of the spinal cord, where it contains autonomic motor nuclei, which are clusters of cell bodies of autonomic motor neurons that regulate the activity of cardiac muscles, smooth muscle, and glands.

Front 25

What are the rami communicantes?

Back 25

Nerve that connects two other nerves. Communicating branches between the anterior ramus of the spinal nerve and the ganglia of the sympathetic trunk. More specifically, it usually refers to one of the following:

- White rami contain sympathetic preganglionic axons (myelinated), that connect anterior ramus with the ganglia of sympathetic trunk. Only the thoracic and first two or three lumbar nerves have white rami communicantes.

- Gray rami contain sympathetic postganglionic axons (unmyelinated) that connect ganglia of the sympathetic trunk to spinal nerves.

Grey rami comm. outnumber (превосходят численно) the white rami.

Front 26

What part of the spinal column can the rami communicantes be found?

Back 26

anterior and lateral to the vertebral column, on both sides

Front 27

What is the primary afferent neuron?

Back 27

Or sensory or receptor neurons - carry nerve impulses from receptors or sense organs toward the CNS. Afferent neurons communicate with specialized interneurons.

Front 28

What do 1st, 2nd and 3rd order neurons refer to?

Back 28

1. First-order neurons conduct impulses from somatic receptor into the brainstem or spinal cord. From the face, mouth, teeth, and eyes, somatic sensory impulses propagate along cranial nerves into the brainstem. From the neck, trunk, limbs, and posterior aspect of the head, impulses travel along spinal nerves into the spinal cord. Their cell bodies are in the dorsal root ganglia or the sensory ganglia of cranial nerves. The central process of these neurons will synapse on 2nd order neurons.

2. Second-order neurons conduct impulses from the brainstem and spinal cord to the thalamus. Axons of 2nd order neurons decussate (cross over to the opposite side) in the brainstem of spinal cord before ascending to the ventral posterior nucleus of the thalamus. Thus, all somatic sensory information from one side of the body reaches the thalamus on the opposite side. These will synapse on cells (third order neurons) located in the thalamus.

3. Third-order neurons conduct

Front 29

What is decussation?

Back 29

crossing over to the opposite side

Front 30

Where do 2nd order sensory neurons originate and terminate?

Back 30

o. - cell bodies are in the dorsal horn or various sensory nuclei of the brainstem.
t. - ventral posterior nucleus of the thalamus.

Front 31

Where do the 3rd order sensory neurons originate and terminate?

Back 31

o. - thalamus
t. - primary somatosensory cortex

Front 32

Where do the upper motor neurons originate and terminate?

Back 32

o. - the motor region of the cerebral cortex or the brain stem
t. - LMN in the ventral horn

Front 33

Where does the lower motor neuron originate and terminate?

Back 33

o. - ventral horn
t. - effector (muscle).

Front 34

What parts of the body are controlled by the visceral system?

Back 34

blood vesscles, the heart, lungs, and the internal organs

Front 35

Compare and contrast the autonomic and somatic systems.

Back 35

1. The somatic nervous system operates under conscious control: the ANS usually operates without conscious control.

2. Sensory input for the SNS is mainly from somatic senses and special senses; sensory input for ANS is from interoceptors, in addition to somatic senses and special senses.

3. The axons of somatic motor neurons extend from CNS and synapse directly with an effector. Autonomic motor pathways consist of two motor neurons in series. The axon of the first neuron extends from CNS and synapses in an autonomic ganglion with the second motor neuron; the second neuron synapses with an effector.

4. The output (motor) portion of the ANS has 2 divisions: sympathetic and parasympathetic. Most body organs receive dual innervation; usually one ANS division causes excitation and the other causes inhibition.

5. SNS effectors are skeletal muscles; ANS effectors include cardiac muscle, smooth muscle, and glands.

Front 36

Where do the autonomic sympathetic neurons originate and terminate?

Back 36

?

Front 37

How many neurons are involved in the autonomic motor nervous system?

Back 37

?

Front 38

What comprises the parasympathetic system?

Back 38

?

Front 39

What are alternative terminations for the 2nd order sensory pathways?

Back 39

?

Front 40

Describe the 3 sensory pathways.

Back 40

- posterior column-medial lemniscus
- anterolateral p/w
- trigeminothalamic p/w

Front 41

What type of information is contained in the pathway that synapses in the dorsal horn?

Back 41

Pain impulses enter the spinal cord, where they synapse primarily on the dorsal horn neurons in the marginal zone and substantia gelatinosa of the gray matter of the spinal cord. This area is responsible for regulating and modulating the incoming impulses. Two different pathways, the spinothalamic and spinoreticular tracts, transmit impulses to the brainstem and thalamus. Spinothalamic input is thought to effect the conscious sensation of pain, and the spinoreticular tract is thought to effect the arousal and emotional aspects of pain.

Front 42

What type of information is contained in the pathway that synapses in the medulla oblongata?

Back 42

Information from the skin, skeletal muscle and joints.

Front 43

What is contained in the posterior column-medial lemniscus pathway?

Back 43

Nerve impulses for touch, pressure, vibration, and conscious proprioception in the limbs, trunk, neck, and posterior head ascend to the cerebral cortex.

Front 44

What is contained in the anterolateral (spinothalamic) pathway?

Back 44

Nerve impulses for pain, temperature, itch, and tickle from the limbs, trunk, neck, and posterior head ascend to the cerebral cortex.

Front 45

What is contained in the trigeminalthalamic pathway?

Back 45

Impulses for most somatic sensations (tactile, thermal, pain and proprioceptive) from the face, nasal cavity, oral cavity, and teeth ascend to the cerebral cortex.

Front 46

What is a nuclei?

Back 46

A cranial nerve nucleus is a collection of neurons (gray matter) in the brain stem that is associated with one or more cranial nerves. Axons carrying information to and from the cranial nerves form a synapse first at these nuclei. Lesions occurring at these nuclei can lead to effects resembling those seen by the severing of nerve(s) they are associated with. All the nuclei excepting that of the IV nerve supply nerves of the same side of the body.

Front 47

What are cuneate and grassile nuclei?

Back 47

Cuneate nuclei - A group of neurons in the inferior part of the medulla oblongata in which axons of the cuneate fasciculus terminate.

Grassile nuclei - a group of nerve cells in the inferior part of the medulla oblongata in which axons of the gracile fasciculus terminate.

Front 48

What are the branches of the trigeminal nerve?

Back 48

The trigeminal nerve (the fifth cranial nerve, also called the fifth nerve, or simply CNV or CN5) is responsible for sensation in the face. Sensory information from the face and body is processed by parallel pathways in the central nervous system.

The fifth nerve is primarily a sensory nerve, but it also has certain motor functions (biting, chewing, and swallowing). These are discussed separately.

The trigeminal nerve is the largest of the cranial nerves.

Three major branches: the ophthalmic nerve (V1), the maxillary nerve (V2), and the mandibular nerve (V3). The ophthalmic and maxillary nerves are purely sensory. The mandibular nerve has both sensory and motor functions.

Front 49

What is a homunculus (sensory cortex map)?

Back 49

A body map based on the amount of cerebral cortex used to process sensory receptors.

Front 50

Describe the corticospinal pathway.

Back 50

(Upper Motor Neurons)
Fibers from precentral gyrus and nearby cortical areas descend through the internal capsule, cerebral peduncles, pons, and pyramids.
Most cross in pyramidal decussation in caudal medulla and form lateral corticospinal tract.
Uncrossed fibers (anterior corticospinal tract) will cross in the anterior white commissure before ending in the spinal gray matter.

Front 51

Describe the corticobulbar pathway.

Back 51

- white matter pathway connecting the cerebral cortex to the brainstem. The 'bulb' is an archaic term for the medulla oblongata; in modern clinical usage, it sometimes includes the pons as well. The word 'bulbar' therefore refers to the nerves and tracts connected to the medulla, and also by association to the muscles thus innervated, those of the tongue, pharynx and larynx.

Function
The muscles of the face, head and neck are controlled by the corticobulbar system, which terminates on motor neurons within brainstem motor nuclei. This is in contrast to the corticospinal tract in which the cerebral cortex connects to spinal motor neurons, and thereby controls movement of the torso, upper and lower limbs.

Front 52

Where does movement initiate?

Back 52

- in the primary motor area of cerebral cortex.

- primary motor area is in the frontal lobe just anterior to the central sulcus