Topic 10: Nervous System

Question 1

Describe the overall structure and work flow of the nervous system

Answer 1

Receptors located in many parts of our body collect information on different functions and changes through sensory pathways to peripheral nervous system.

The central nervous systems receives info, processes it, and sends instructions to the peripheral nervous system then through motor pathways to either autonomic or somatic nervous system.

Autonomic controls unvolunteer processes.
Somatic controls things that we can do voluntarily.

Autonomic nervous system consists of sympathetic and parasympathetic division which will trigger effectors to do the work or change the conditions. These changes will be received by the receptors.

Question 2

What pathways deliver info into the CNS and out of the CNS?

Answer 2

• Afferent pathway: carrying information from receptors to CNS (sensory division of PNS)
• Efferent pathway: carrying instructions from CNS to effectors (motor division of PNS)

Question 3

Describe the structure of the brain

Answer 3

The brain can be divided into 2 parts
- Forebrain: the largest region
+ The most important part: cerebrum, controlling the most complex processes and located at the top of the brain
+ Underneath that is thalamus, hypothalamus, pineal gland and limbic system

• Hindbrain: more primitive, but vital functions
  + Includes midbrain, brainstem, cerebellum
  + Cerebellum: fine control of movement
  + Brainstem
  ~ pons: control information distribution to other regions
  ~ medulla oblongota: brain transition to spinal cord

Question 4

Describe the structure of the brain

Answer 4

The brain can be divided into 2 parts
- Forebrain: the largest region
+ The most important part: cerebrum, controlling the most complex processes and located at the top of the brain
+ Underneath that is thalamus, hypothalamus, pineal gland and limbic system

• Hindbrain: more primitive, but vital functions (breathing, heart beating)
  + Includes midbrain, brainstem, cerebellum
  + Cerebellum: fine control of movement
  + Brainstem: ~ pons: control information distribution to other
  regions
  ~ medulla oblongata: brain transition to spinal
  cord

Question 5

Describe the structure and characteristics of the cerebral cortex

Answer 5

The cerebral cortex is the highest functioning part of brain (physical location and functional)
Divided into left and right hemispheres connected by corpus callosum.
Each hemisphere has 4 lobes: frontal, parietal, temporal, occipital
Each area of the brain has different functions

Question 6

List the components of CNS and PNS

Answer 6

• CNS: the brain and the spinal cord
• PNS: cranial and spinal nerves

Question 7

Describe the general functions of each lobe

Answer 7

• Frontal lobe: responsible for higher executive functions, main decision-making area
• Parietal lobe: important sensory area (touch, temperature, pressure, pain)
• Temporal lobe: important sensory area (hearing, language, memory)
• Occipital: visual information

Question 8

Describe the functions of the cerebellum

Answer 8

The cerebellum controls our movement and maintains posture by controlling muscles tone and voluntary muscles activity.

It does NOT initiate movement.

It uses information and instructions moving up and down in sensory and motor pathways to finetune movement.

It receives information about balance from vestibular system.

Question 9

Describe the brainstem

Answer 9

The brainstem is located at the lowest part of the brain.
- connects the cerebrum to the spinal cord and the cerebellum
- many afferent and efferent tracts
- responsible for many functions: breathing, consciousness, blood pressure, heart rate & sleep

Question 10

Describe the spinal cord and spinal nerves

Answer 10

The spinal cord is a part of CNS, connecting brain with PNS and bringing motor/sensory signals.
- Controller for many reflexes without the need of the brain (spinal reflexes)
- Contained in the vertebral column and divided into many segments corresponding to each vertebrae
- Pairs of spinal nerves emerge from spinal cord between vertebrae, carrying both sensory/motor info
- Have white matter outside and grey matter inside

Spinal nerves are nerves emerging from the spinal cord with 2 roots: ventral or efferent and dorsal or afferent
Each spinal nerve controls functions in different body parts.

Question 11

What are white and grey matter?

Answer 11

• White matter: fibre tracts of myelinated sensory and motor axons where information goes through
• Grey matter: neuron cell bodies

Question 12

Explain decussation

Answer 12

Decussation is when pathway cross-over as traveling across CNS.
Both sensory and motor pathways decussate from 1 side of CNS to other –> each hemisphere receives info and controls actions of the opposite body side

Question 13

What are peripheral nerves?

Answer 13

Peripheral nerves are large anatomical nerves making up of many spinal nerves joining.
Many nerve fibres, both motor and sensory, delivering information in correct tracts to the spinal cord.

Question 14

What are cranial nerves?

Answer 14

The cranial nerves arise directly from the brain and brainstem (control processes on face and head)

Question 15

Describe functions of autonomic nervous system

Answer 15

Responsible for involuntary control of functions and maintaining homeostasis.
Controls cardiac muscle, smooth muscle, exocrine glands, endocrine glands.

Question 16

Describe the divisions of autonomic nervous system

Answer 16

• Sympathetic: activated when under stress, “fight or flight”
  i.e: heart beating faster, airways getting larger, increased blood pressure, etc.
  + secrete substances/hormones to cope with stress
• Parasympathetic: “rest and digest”, when relaxed
  + NOT release hormones
  + more focused and specific reactions

Question 17

Describe the structure and function of a neuron

Answer 17

Neurons are the basic structure unit of the CNA, not the only one but take up most.
Each neuron is an individual cell which communicate with others at synapes.

A neuron has cell body, dendrites and axons.
- Dendrites: receive information from many cells
- Axons (1 axon and many axon terminals): generate action potential, transmite information and branch to communicate with other cells

Question 18

Explain the role of cell membrane and integral membrane proteins in the CNS

Answer 18

Cell membrane is made up of phospholipid molecules so substances with low lipid solubility cannot pass through without integral membrane proteins like leak channels, gated channels and pumps.

These channels, especially the gated channels and pumps and responsible for the movement of Na+ and K+ ions which generate the cell membrane potential and action potential in the CNS.

Question 19

Explain how cell membrane potential develops

Answer 19

The membrane is most permeable to K+, but not to Na+.
K+ ions move along the concentration gradients, making the inside of the cell more negative, creating a membrane potential.

Eventually, concentration gradient and electrical gradient will be balanced, reaching equilibrium. The electrical gradient remains stable, resting membrane potential, until something triggers changes.

Question 20

How do voltage gated channels react to changes in membrane potential?

Answer 20

• At resting potential, negative: the channels close
• At increasing potential, more positive: the channels gradually open

Question 21

Explain the concept of action potential and how it is generated

Answer 21

Action potential is the overall electrical change in a neuron or the way electrical information is transmitted through NS.

At resting potential, the cell membrane potential is negative. Once there is a stimulus, some Na+ channels will open until the potential reaches a threshold at which all Na+ channels will open, Na+ ions rush into the cell, the soma end of the axon become depolarized and increase the voltage.
The depolarization spreads down the axon and the soma end become repolarized as all Na+ channels close while K+ channels open, K+ ions move out of the cell, repolarize the cell membrane.
The action potential continues down the axon until it reaches the axon terminal where neurotransmission occurs.

Question 22

Stronger stimulus triggers what in the action potential?

Answer 22

Stronger stimulus triggers an increased frequency of action potential

Question 23

Explain Myelin and its function

Answer 23

Myelin is an insulated sheets wrapping around segments of the axons, which is made up of 80% lipid and make what is called the white matter.
Myelin helps to increase the speed of nerve conduction.

Question 24

What is node of Ranvier?

Answer 24

These are the gaps in between myelinated axons where action potential occurs.

Question 25

Describe the factors affecting speed of transmission in a neuron

Answer 25

The diameter of fibre type and whether it is myelinated or not affect the speed of transmission in a neuron.

Question 26

Explain synapse and neurotransmitters

Answer 26

Synapse is the gap between 2 nerves where communication occurs and information is transmitted.

Neurotransmitters are chemical messengers syntesized in neuron cell bodies, transfered to the end of axons and stored at the axon terminal or the presynaptic neuron.

Question 27

Explain the process of neurontransmission

Answer 27

The 2 nerves are not physically, but chemically in contact.

Action potential moves along the axon towards the axon terminal, triggering a rush of Ca+ into the neuron and releasing neurotransmitters from synaptic vesicles.

Neurotransmitters diffuse across synaptic cleft to bind with receptors on the post synaptic membrane or the start of dendrites to trigger a change or action.

Question 28

Explain the role of receptors and enzymes in synaptic function

Answer 28

• Receptors on the postsynaptic membrane bind to neurotransmitters to receive chemical messengers.
• Enzymes help to break down neurotransmitters after their job is done.

Question 29

Define EPSPs and IPSPs and explain how they are generated

Answer 29

• Exhibitory post synaptic potentials is inputs that depolarize post synaptic cells, helping the membrane to reach the threshold for depolorization and trigger action potential. This can be done via exhibitory neurotransmitters like Glutamate.
• Inhibitory post synaptic potentials is inputs that repolarize the cell membrane and make it less like to generate action potential. This can be done via inhibitory neurotransmitter like GABA.

Question 30

Explain temporal summation and spatial summation and why we need these processes

Answer 30

• Temporal summation is the add on of many action potentials over a short period of time.
• Spatial summation is when post synaptic nerves receive informtion from different nerves simultaneously.

1 action potential is not enough to generate any changes or actions so we need a summation of action potentials.