Khan Academy

Question 1

How many cranial nerves are there? Spinal?

Answer 1

Cranial = 12
Spinal = 31

Question 2

What are ganglia?

Answer 2

Collections of neuron somas

Question 3

Nerves come in pairs of afferent and efferent nerves. What is the function of each of these nerves?

Answer 3

Afferent = carry sensory information to the CNS
Efferent = carry motor information away from CNS

** to remember: think Exit Efferent

Question 4

Afferent and efferent nerves in the spine are paired on either side of the spinal column, with one nerve anterior and one nerve posterior. Which nerve is which? (I.e are efferent nerves anterior or posterior?)

Answer 4

Efferent nerves are anterior, afferent nerves are posterior

** to remember: Exit through the front door
Efferent neurons are in front (anterior)

Question 5

What are the components of a motor unit?

Answer 5

1) lower motor neuron

2) skeletal muscle cell(s) that the neuron synapses with (is in electrical contact with)

Question 6

What is the name for a synapse in a motor unit?

Answer 6

Neuromuscular junction

Question 7

Imagine a motor unit in the front of your leg and a motor unit in your fingers. How are these motor units similar? How are they different?

Answer 7

Similar:
- still consist of motor neuron in spine and muscle cells that it controls

Different:
- size of motor unit is related to function of skeletal muscle: the fingers have smaller muscles that perform intricate movements, whereas the quadriceps of your leg is a large muscle that perform much less intricate movements. Therefore, the motor units that enervate the hands are smaller (less skeletal muscle cells under the control of one neuron) than those that enervate the leg (more skeletal muscle cells under the control of one neuron)

Question 8

There are several basic abnormalities that can occur to lower motor neurons. These abnormalities are called Lower Motor Neuron Symptoms (LMNS) (** think lemons). What are these symptoms?

Answer 8

1) weakness
2) atrophy (decreased muscle bulk)
3) hypotonia (decreased muscle tone, muscle tone is the resting tension in our muscles, if a person displays hypotonia then their muscles seem very relaxed when at rest and do not display much resistance to manipulation)
4) hyporeflexia = decreased muscle stretch reflexes, which are reflexes that happen if you rapidly stretch the muscle
5) Fasiculations = twitches that are constant and occur in an isolated area

Question 9

What does somatosensation refer to?

Answer 9

Sensory information collected by the PNS

Question 10

What are the 5 kinda of somatosensation? For each kind of sensation, what is the name of the reception associated with sensing the sensation?

Answer 10

1) position (mechanoreceptor)
2) vibration (mechanoreceptor)
3) touch (mechanoreceptor)
4) pain (nociceptor)
5) temperature (thermoreceptors)

Question 11

What is a distinguishing feature of mechanoreceptors?

Answer 11

They tend to be closer to the surface of the skin and contain a bulbous structure at their free end.

Question 12

How do the axons of mechanoreceptors compare to those of nociceptors and thermoreceptors?

Answer 12

The axons of mechnoreceptors are larger in diameter and have a thicker myelin shealth, which means they conduct action potentials more rapidly

Question 13

Muscle Stretch Reflex (MSR)

1) What are the 2 basic parts of this reflex (and really any relfex)?
2) What is the characteristic feature of reflexes (general)?
3) In MSR, what side of the body are the signals on?

Answer 13

1) A stimulus (mallet) to the patellar tendon causes afferent somatosensory axon to send a signal to its soma near spinal cord, which creates an excitatory state. Then, efferent neuron, with soma in spinal cord, responds to excited state by sending signal to its axon to contract quadriceps. This results in production of a moment about the knee joint, which results in kicking of the lower leg.
2) They are involuntary action, do not require involvement of the cerebrum.
3) Afferent signal and efferent response are on the same side of the body.

Question 14

What is a major difference between the way that efferent sympathetic and parasympathetic neurons synapse?

Answer 14

Efferent sympathetic NS neurons have soma in spinal cord, then have short axon that synapses on a nearby ganglia, which then has long axons that synapse on the tissue.

Efferent parasympathetic NS neurons have soma in the spinal cord and long axons that travel all the way to other neurons in/near the tissue. Once at the tissue, the axon synapses with the soma of another neuron, which has an axon in the tissue.

Question 15

What are the targets of the autonomic nervous system?

Answer 15

Glands
Smooth muscle
Efferent neurons
Cardiac muscle

Question 16

What is grey matter? White matter?

Answer 16

Grey matter contains somas

White matter contains myelinated axons

Question 17

In the spinal cord, where is grey matter concentrated? White matter?

Answer 17

In the spinal cord, grey matter is concentrated in the center of the cord in an ‘H’ or butterfly shape. White matter surrounds the grey matter.

Question 18

In the brain, where is grey matter? White matter?

Answer 18

Grey matter is mostly on the outer surface of the brain (there are some bodies of grey matter in the brain called nuclei, such as the septal nuclei). White matter is mostly in the middle of the brain.

This is opposite of the spinal cord.

Question 19

Where are upper motor neurons contained? What do they synapse on?

Answer 19

They are in the grey matter of the brain, their axons travel through the white matter of the brain and synapse on the lower motor neurons

Question 20

Describe the corticospinal tract

Answer 20

UMN Soma in the left hemisphere have axons that travel down through the brain, cross the midbrain, pons and medulla and synapse on LMN somas on the right side of the spinal cord

Question 21

What is a major difference between the way that efferent sympathetic and parasympathetic neurons synapse?

Answer 21

Efferent sympathetic NS neurons have soma in spinal cord, then have short axon that synapses on a nearby ganglia, which then has long axons that synapse on the tissue.

Efferent parasympathetic NS neurons have soma in the spinal cord and long axons that travel all the way to other neurons in/near the tissue. Once at the tissue, the axon synapses with the soma of another neuron, which has an axon in the tissue.

Question 22

What are the targets of the autonomic nervous system?

Answer 22

Glands
Smooth muscle
Efferent neurons
Cardiac muscle

Question 23

What is grey matter? White matter?

Answer 23

Grey matter contains somas

White matter contains myelinated axons

Question 24

In the spinal cord, where is grey matter concentrated? White matter?

Answer 24

In the spinal cord, grey matter is concentrated in the center of the cord in an ‘H’ or butterfly shape. White matter surrounds the grey matter.

Question 25

In the brain, where is grey matter? White matter?

Answer 25

Grey matter is mostly on the outer surface of the brain (there are some bodies of grey matter in the brain called nuclei, such as the septal nuclei). White matter is mostly in the middle of the brain.

This is opposite of the spinal cord.

Question 26

Where are upper motor neurons contained? What do they synapse on?

Answer 26

They are in the grey matter of the brain, their axons travel through the white matter of the brain and synapse on the lower motor neurons

Question 27

Describe the corticospinal tract

Answer 27

UMN Soma in the left hemisphere have axons that travel down through the brain, cross the midbrain, pons and medulla and synapse on LMN somas on the right side of the spinal cord

Question 28

Describe the corticobulbar tract

Answer 28

Soma of UMN in the grey matter on one side of the brain have axons that cross the white matter and hind brain in the same way that they do in the corticospinal tract to synapse on LMN on the opposite side of the brain stem, but those same axons also split and synapse on LMN on the same side of the brain stem as their own soma.

Question 29

Imagine a UMN on the left side of the brain that synapses on a LMN on the right side of the spinal cord.

If the LMN is damaged, how would symptoms present?

If the UMN is damaged?

Answer 29

If LMN damaged, symptoms will present on the same side of the body as LMN

If UMN is damaged, it depends on where it was damaged. If damaged before crossing hind brain, symptoms will present on side of body opposite the damaged site of UMN (ie damaged on left soma = weakness in right muscle). If damaged after crossing hind brain, symptoms will present on the same side of the body as the damaged site of UMN (ie if damaged on UMN axon which is on right side of body then weakness in right muscle)

Question 30

What are the 4 signs of upper motor neuron damage?

Answer 30

1) hyper - reflexia (increased muscle stretch reflex, ie knee kicks out farther when hit with mallet)
2) clonus (rhythmic contraction of antagonist muscles)
3) hypertonia (increased base line resistance to manipulation)
4) extensor plantar response (if stimulate bottom of foot with solid object, toes normally curl toward object but in this symptom toes would curl away and upward instead)

Question 31

In general terms, there are two large somatosensory tracts. Each tract contains axons that travel to the same location. These two tracts sense different things. What are the two major groupings of senses that travel together?

Answer 31

1) position, vibration, fine touch

2) pain, temperature, gross touch

Question 32

What are the basic functions of the reticular formation?

Where is it located?

What would injury to this area result in?

Answer 32

(1) To filter incoming sensory information
(2) plays a role in arousal / sleep-wake

It is located in the brain stem behind medulla

Injury may result in coma