Week 2: Nervous System

Question 1

what is the central nervous system

Answer 1

• everything inside the spine and skull
• the cortex
• subcortical structures and nuclei
• spinal cord
• the structures are encased in bone
• they are very poor at fixing themselves if damaged

Question 2

what is the peripheral nervous system

Answer 2

• everything outside the spine and skull
• unlike the CNS, the PNS is plastic (e.g. it can regrow after damage)
• input from the sensory division (afferent)
• output from the motor division (efferent)

Question 3

what are nerves

Answer 3

bundles of axons that connect the body to the rest of the body

Question 4

what are ganglions

Answer 4

clusters of cells

Question 5

what is the somatic nervous system

Answer 5

• controls voluntary movement
• conducts impulses from the CNS to skeletal muscles

Question 6

what is the automatic nervous system

Answer 6

• controls involuntary movements
• conducts impulses from the CNS to cardiac muscles, smooth muscles and glands

Question 7

what is the somatic motor system (efferent)

Answer 7

• peripheral nerves exit the spinal cord and contact muscles
• stimulation of these nerves causes contraction of muscle and moves the body

Question 8

what is the autonomic motor system (efferent)

Answer 8

• controls the lung, the heart, smooth muscle, and exocrine and endocrine glands
• works together to keep the internal system in balance

Question 9

what is the difference between the sympathetic and parasympathetic nervous system

Answer 9

• a complex system with many functions
• parasympathetic: “rest and digest”
• sympathetic: “fight or flight”

Question 10

what is included in the basic sensory system

Answer 10

• visual
• auditory
• olfactory (smell) system
• gustatory (taste) system
• tactile system
• vestibular (sense of head movement in space) system
• proprioceptive (sensations from muscles and joints of body) system

Question 11

why are movements like a circuit

Answer 11

• all movements really start in the sensory domain
• movements tend to be either:
  
  • in response to an external stimulus (saving the penalty)
  • directed at an external stimulus (taking the penalty)
• either way they start with a sensory input

Question 12

what are sensory inputs

Answer 12

• receptors monitor changes
• changes called ‘stimuli’
• information sent by ‘afferent’ nerves

Question 13

what is integration

Answer 13

• info processed
• decision made about what should be done

Question 14

what is motor output

Answer 14

• effector organs (muscles or glands) activated
• effected by ‘efferent’ nerves

Question 15

what is a neuron

Answer 15

nerve cells that are electrically excitable cells and communicate with other cells via specialised connections called synapses - they make up the majority of nervous tissue

Question 16

what are glial cells

Answer 16

non neuronal cells in the nervous system that maintain homeostasis, form myelin, and provide support and protection for neurons

Question 17

what does a cartoon neuron look like

Answer 17

• neurons typically have a cell body that contains the nucleus
• the cell body has filaments on it called dendrites. these often branch profusely, but only a few hundred micrometers from the cell
• a single long projection originate from the cell body - this is the axon. the axon can only be a few mm long but can be over a metre in humans and much longer in other animals
• the axon can be covered in myelin - a fatty sheath that makes electrical signals pass more quickly
• the axon ends in the axon terminal. these contract the dendrites of other neurons and so information is passed through the nervous system
• bundles of axons are what makes up nerves

Question 18

what is the structure of a neuron

Answer 18

• in real life, neurons come in many shapes and sizes dependent on function though virtually all still contain dendrites and axons, and all have a cell body
• the dendritic pattern indicates the number of inputs (and the information) received by a neuron

Question 19

what are action potentials

Answer 19

• signals arrive at the dendrites - these signals change the electrical charge of the cell (up and down)
• if the charge reaches a set point/threshold, an action potential occurs and travels down the axon
• this is a single punctate event, so information is coded by the rate of firing of action potentials

Question 20

why is information that is passed between neurons chemical

Answer 20

• when an action potential reached the axon terminal it causes calcium to enter the terminal
• this causes synaptic vesicles containing neurotransmitters to bind to the cell membrane and release their contents into the synaptic cleft
• the neurotransmitter binds to specialist receptors on the dendrites of the next neuron
• if the neurotransmitter is inhibitory this lowers the charge in the receiving neuron, if the neurotransmitter is excitatory it increases the charge in the receiving neuron
• if the charge in a receiving neuron passes the threshold the neuron will fire an action potential

Question 21

what are the different types of glial cells

Answer 21

• astrocytes
• oligodendrocytes
• schwann cell
• microglia
• ependymal cells

Question 22

what are astrocytes

Answer 22

• astrocytes
  
  • regulate chemicals around neurones
    
    • regulate glucose
    • regulate ion concentrations
    • neurotransmitter uptake
  • regulate blood flow around the brain
    
    • vasomodulation
  • nerous system repair
    
    • following injury astrocytes fill spaces in the nervous system creating glial scars
  • maintenance of the blood-brain barrier

Question 23

what are oligodendrocytes

Answer 23

• form the myelin sheath on axons in the central nervous system
• myelin is a fatty, protein rich sheath that wraps around axons
• each oligodendrocyte can myelinate up to 50 axons

Question 24

what are schwann cells

Answer 24

• form myelin in the peripheral nervous system
• assist in regerneration and regrowth of axons
• myelin allows axon potentials to propagate more quickly
• unmyelinated speeds - 0.5 to 10m/s
• myelinated speeds - 150m/s

Question 25

what are microglia

Answer 25

• are the brains immune system
• scavenge the central nervous system for plaques, damages cells and infectious agents

Question 26

what are ependymal cells

Answer 26

make up a membrane called the ependyma, which is a thin membrane lining the central canal of the spinal cord and the ventricles they produce cerebrospinal fluid

Question 27

what is the difference between grey and white matter

Answer 27

• myelin is a sheath that insulates many neurons
• it is made of fat and proteins and is white
• because if this, parts of the brain that are many made of axons are white (white matter)
• the areas of the brain that contains mainly the cell bodies of the neurons - nuclei, ganglion, cortex - appear pink in the fresh tissue but grey in the perfused (grey matter)