Lecture 19 - Central Nervous System

Question 1

Central Nervous System (CNS):
- what are the two parts to the CNS?

Answer 1

Slide 6
Brain and spinal cord

Question 2

Peripheral Nervous system (PNS):
- what is included in the PNS (2)
- what are the two types of nervous systems in the PNS? what is a sub-nervous system for one of them?
- state what each nervous systems function is and any important info - like what muscles it uses or where it may receive its input from?

Answer 2

slide 7

• the PNS includes (1) all neurons, and (2) parts of neurons outside the CNS (axons may be in the CNS, where cell bodies are in PNS – thus parts of neurons)
• PNS is made up of the somatic nervous system and the autonomic nervous system. the enteric nervous system is a subcategory of the autonomic nervous system.
• somatic NS: conscious, controlling voluntary action via skeletal muscle
• autonomic NS: unconscious, controls visceral functions such as heart rate and breathing
• enteric NS: controls digestion and movements of the gut. It gets input from spinal cord, but can also work independently.

Question 3

Number of neurons:
- which has more neurons: CNS or PNS
- how many neurons are there in the brain, spinal cord and enteric nervous system/PNS
- what are glia and what is their function and number in the body?

Answer 3

slide 8

• the CNS has more neurons
• neuron number –> CNS: brain = 86 B, spinal cord = 1B, PNS: enteric/whole PNS = 100-600 M
• glia or glial cells support and protect neurons in the CNS and PNS. they are as numerous.

Question 4

Ventricles:
- what are ventricles and where are they present (which nervous system)?
- list the 3 ventricles and 1 canal – top to bottom connection

Answer 4

slide 9-10

• ventricles are regions in the brain that are filled with cerebrospinal fluid (CSF). Therefore, are a part of the CNS
• lateral ventricle –> third ventricle –> fourth ventricle –> central canal of spinal cord

Question 5

Gray and White Matter:
- what is grey matter
- what is white matter
- what is grey matter in CNS called vs PNS
- what is white matter in CNS called vs PNS

Answer 5

slide 11

• grey matter: unmyelinated axons/dendrites in layers/clusters
• white matter: myelinated axons running in bundles
• name for grey matter: CNS = nuclei, PNS = ganglia
• name for white matter: CNS = tracts, PNS = nerves

Question 6

Brain and Energy consumption:
- what percent of blood from the heart and fraction of glucose does the brain take?
- what is the percent mass of the brain in the body?
- how is the brain energy efficient when compared to computers that mimic the brain? how many watts does the brain run on?

Answer 6

slide 12-13
- the brain consumes half of the body’s glucose and 15% of the hearts blood
- the brain is only 2% of body mass
- the brain is energy efficient as it needs about 40 watts to operate (like a lightbulb), whereas computational computers that mimic the brain need much more energy.

Question 7

CNS and saving energy:
- how do neurons communicate with each other? what is the con of this communication method?
- what general rate of firing can the energy supply to the CNS support? ex. in the cortex, one spike is given in how many seconds?
- at any moment, what percent of neurons are firing?
- what does this all mean?

Answer 7

slide 14
- neurons communicate via action potentials. but these action potentials take a lot of energy.
- the energy supply to the CNS can support a low rate of firing. ex. in the cortex,there is an average rate of just 1 spike/6s for one cell.
- thus, only ~4% of your neurons are firing at any moment.
- That is, communication is expensive, and so the CNS has to use it sparingly by limiting communication between neurons.

Question 8

Spinal cord:
- how many spinal cord segments are there and associated spinal nerves?
- what is the dorsal root? what signal does it carry? direction?
- what is the ventral root? what signal does it carry? direction?
- what does the dorsal root ganglion hold?

Answer 8

slide 16
- 31 spinal cord segments and associated spinal nerves
- dorsal (back) root: carrying afferent (incoming) information (PNS –> CNS)
- ventral (front) root: carrying efferent (outgoing) information (CNS –> PNS)
- dorsal root ganglion: cell bodies of the neurons carrying the afferent information

Question 9

spinal cord:
- where is gray matter and white matter in the cord?
- what are the two sections (horns) of the grey matter in the spinal cord called?

Answer 9

slide 17
- the grey matter is in the middle of the cord in a butterfly shape and the white matter is on the outside of the cord
- the butterfly grey matter is split into two parts: dorsal horn (top/back), ventral horn (bottom, front)

Question 10

grey matter in spinal cord:
- what are the two types of nuclei in each horn of grey matter called?
- where is the signals received or released to?

Answer 10

slide 18
the grey matter consists of sensory and motor nuclei (CNS grey matter)
- dorsal horn: (1) somatic sensory nuclei, (2) visceral sensory nuclei
- ventral horn: (1) somatic motor nuclei, (2) autonomic efferent nuclei

Dorsal:
- somatic sensory nuclei: get signals from skin
- visceral sensory nuclei: get signals from the viscera (internal organs)

Ventral:
- somatic motor nuclei: send commands to skeletal muscles
- autonomic efferent nuclei: send commands to glands and smooth muscles

Question 11

white matter in spinal cord:
- what are the three tracts in the white matter of spinal cords?
- where do they carry signals to/from?
- which horn are each of the tracts found in mainly?

Answer 11

slide 19
- (1) ascending tracts, (2) descending tracts, (3) propriospinal tracts
- ascending tracts: carry sensory signals TO the brain. mainly dorsal (sensory afferent signals are dorsal)
- descending tracts: carry sensory signals FROM the brain. mainly ventral (efferent signals are ventral)
- propriospinal tracts: stay in the spinal cord, may send signals up or down it

Question 12

spinal reflexes:
- what is a spinal reflex?
- when is a spinal reflex conducted?
- how is the knee-jerk-reflex an example of a spinal reflex?
- what is the shortened pathway for a spinal reflex?

Answer 12

slide 20
- spinal reflex is when the spinal cord responds to stimuli without consulting the brain
- this happens when a very fast reflex must be conducted
- knee-jerk-reflex: if the ligament below the kneecap is hit, sensory neurons send this information to the dorsal horn (somatic sensory nuclei). These fibers send branches up to the brain, but also excite neurons in the ventral horn (somatic motor nuclei) that send signals out to leg muscles to contract and counter the stretch.
- afferent somatic sensory input –> dorsal horn –> interneuron –> ventral horn –> efferent somatic motor output
- afferent somatic sensory input –> dorsal horn –> to the brain

Question 13

brain divisions:
- what are the 6 major divisions of the brain and where are they located?

Answer 13

slide 22
- cerebrum
- diencephalon
- midbrain
- pons
- medulla
- cerebellum

see diagram

Question 14

brain stem:
- what are the three divisions of the brain that makes up the brain stem?
- what is the brain stem responsible for?
- which cranial nerves arise from the brain stem?

Answer 14

slide 23
- brain stem consists of the midbrain, pons, medulla. the thalamus is on top of the brain stem.
- function: main control center for many autonomic functions and reflexes, such as breathing, swallowing, vomiting, and regulating blood pressure.
- cranial nerves 3-10 and 12 arise from the brain stem

Question 15

cranial nerves:
- how main cranial nerve pairs are there?
- what do cranial nerves do? compared to spinal segments?

Answer 15

slide 24
- there are 12 pairs of cranial nerves
- Cranial nerves are nerves that enter or leave the brain. (CNS –> PNS) or (PNS –> CNS)
- like the than the spinal cord segments which consist of nerves that enter or leave the spinal cord

Question 16

diencephalon:
- which brain regions comprise of the diencephalon (4)
- what is the function for each brain region?

Answer 16

slide 25
- diencephalon: thalamus, hypothalamus, pituitary gland, pineal gland. the corpus callosum in the cerebrum is above this region.
- Thalamus: processes information going to and from the cerebral cortex in the cerebrum. ie. mediator for sensory information.
- Hypothalamus: regulates behavioral drives, and endocrine and autonomic homeostasis.
- Pituitary and pineal glands: secrete hormones.

Question 17

cerebrum:
- what are the 2 hemispheres in the cerebrum connected by? what is this region made up of?
- what is the cerebral grey matter made up of (3)
- where is the grey and white matter concentrated in the cerebrum vs the spinal cord?

Answer 17

slide 26
- The cerebrum is the largest part of the brain, encompassing both the left and right hemispheres. the 2 hemispheres are connected by the corpus callosum which is made up of a bundle of myelinated axons (white matter = tract in CNS)
- the cerebral grey matter is made of (1) cerebral cortex, (2) limbic system, (3) basal ganglia (should be called nuclei - controls movement)
- cerebrum = grey outside, white inside – spinal cord = grey inside, white outside

Question 18

cerebral lateralization:
- what is cerebral lateralization?
- what is the left (4) vs right (2) hemisphere responsible for?

Answer 18

slide 27
- we have cerebral lateralization which is where the 2 hemispheres have different functions
- left hemisphere: language, math, speech, writing
- right hemisphere: analysis by touch, spatial analysis

Question 19

brain lobes + cingulate gyrus:
- what are the 4 lobes of the brain and where are they located generally?
- where is the cingulate gyrus of the limbic system located if see the brain internally?

Answer 19

slide 28-29
- 4 lobes: frontal, temporal, pariteral, occipital
- the cingulate gyrus spans the bottom of the frontal lobe and a bit of the parietal lobe – above the corpus callosum

Question 20

limbic system:
- what are the three brain regions in the limbic system?
- what is the limbic system responsible for? how does the example study with lesioned monkeys and snakes explain some functions?

Answer 20

slide 30
- limbic system: (1) cingulate gyrus, (2) hippocampus, (3) amygdala
- function: concerned with motivation, emotion, and memory
- ex. monkeys with amygdala lesions, unlike normal monkeys, are not frightened of snakes.