Week 3

Question 1

Neurons

Answer 1

Neurons are specialised cells capable of generating electrochemical impulses between neurons and other cells to communicate with other cells, transduce and transfer information and to bring about physiological changes to the body

Question 2

Neuron Anatomy

Answer 2

Dendrites - Branched extensions located above the soma that are responsible for receiving electrochemical signals from other neurons or cells and transfer it towards the axon.

Soma (Cell body ) - contains nucleus, mitochondria, ER etc.

Axon Hillock (Initial Segment) : A thick unmyelinated section between the soma and axon that is responsible for the generation of action potential

Axon: The long, thin portion of the neuron that transfers electrochemical signals to the axon terminal

Myelin Sheaths: Insulators that cover majority of the axon to improve the efficiency of impulse communication. Made up of oligodendrocytes (CNS) or Schwann cells (PNS).

Nodes of Ranvier: Unmyelinated small segments on the axon responsible for the regeneration of action potential.

Axon Terminal: Location of transfer of electrochemical signals to other neurons or cells. Is the pre-synaptic portion of the synapse.

Question 3

Meninges

Answer 3

The meninges refers to the protective layer of bone (cranium) and connective tissue layers that insulates the brain and spinal cord (vertebral column)
- Dura mater: Outer layer directly adhered to the cranium. Made up of tough, fibrous connective tissue.
- Arachnoid mater: Middle layer located between the dura mater and pia mater. Contains the subarachnoid space, filled with cerebrospinal fluid (CSF) responsible for providing more cushioning and nutrients to the brain.
-Pia mater: Thin inner layer of connective tissue directly attached to brain tissue

Question 4

Central Nervous System (CNS)

Answer 4

• Brain and spinal cord

Question 5

Peripheral Nervous System (PNS)

Answer 5

• spinal or peripheral nerves

Question 6

Neuroglia

Answer 6

Non-neuronic cells located within the nervous system that aids in neuron functioning.
- Astrocytes: Responsible for transporting nutrients such as glucose from blood vessels to neurons.
- Oligodendrocytes & Schwann Cells: Makes up myelin sheaths in CNS and PNS respectively that surround and insulate the axons of neurons.
- Microglia: Immune cells within the CNS that phagocytose pathogens or infected cells
- Ependymal cells: Lines the ventricles (fluid filled cavities) of the brain and the central canal of the spinal cord. Also contributed to the production of CSF

Question 7

Grey Matter

Answer 7

• Greyish pink colour comes from Nissl bodies (protein synthesis organelles, rough ER, ribosomes)
• Location of connections between neurons
• Made up of cell body and dendrites of neurons in the CNS and some glia

Question 8

White Matter

Answer 8

-Made up of axon of CNS neurons
- White due to high lipid content in myelin sheaths (oligodendrocytes)

Question 9

Neural Tissue Organisation

Answer 9

Brain: Grey matter outside, white matter inside
Spinal Cord: White matter outside, grey matter inside

Question 10

Blood Supply to the Brain

Answer 10

• The brain recieves 15% of the blood supply
• THis is due to the high energy requirement of neurons. (high metabolic rate)
• The brain recieves 20% of blood oxygen and 50% blood glucose to enable rapid ATP generation (efficient signalling probs)
  -The brain cannot store glucose like other cells and relies on astrocytes to transport

Question 11

Blood Brain Barrier

Answer 11

-Capillaries are thin blood vessels throughout the body and brain which transport nutrients.
- Capillary walls are made up of a single layer of cells called endothelial cells which typically contain pores to allow nutrients to ensure easy transportation
- However endothelial cells in the brain are held by tight junctions, known as the blood brain barrier
- This prevents pathogenic, drugs or other harmful substances from entering the brain (as neurons do not regenerate and can lead to severe holistic health issues)
- However it prevents the transportation of nutrients. Astrocytes act as specialised transporters, making a semi-permeable membrane formed to only allow certain molecules to neurons.

Question 12

Cerebral Hemispheres

Answer 12

Largest region of the brain. Grey matter running across the surface known as the cerebral cortex. Contains 16 billion neurons.

86 billion neurons in the whole brain

Surface of the brain is highly folded in order to increase SA to maximise area for neurons.
- Gyrus (Gyri)- Bumps
- Sulcus (Sulci) - depressions or ridges

-Frontal
- Temporal
- Parietal
- Occipital

Question 13

Frontal Lobe

Answer 13

Responsible for:
- behaviour, emotions
- voluntary motor control
- personality traits
- reasoning, decision-making, problem solving, planning

Question 14

Parietal Lobe

Answer 14

Responsible for:
- Detects and integrates sensory signals and generates efferent signals to help coordinate movement (Contains the somatosensory and gustatory cortex)

Question 15

Temporal Lobe

Answer 15

Responsible for:
- Processing auditory information
- Comprehending language
- Memory formation and retrieval
- Recognition of objects
- Emotional Responses
(Contains auditory and olfactory cortex)

Question 16

Occipitial Lobe

Answer 16

Responsible for:
- Processing and interpretation of visual information

Question 17

Cerebellum

Answer 17

Smaller region of the brain, 10% of its volume but contains 80% of neurons.

Responsible for:
- Maintaining balance and posture
- Motor learning
- Controls eye movements
- Coordinates the timing and force of muscle contractions

Question 18

Brainstem

Answer 18

Composed of:
- Midbrain
- Pons
- Medulla Oblongata
Controls numerous essential funcitons:
- Cardiac function
- Eating
- Sleeping
- Respiration
- Consciouosness/Alertness

Question 19

Cranial Nerves

Answer 19

12 cranial nerves that control sensory reception. e.g. olfactory, optic (smell and sight_ respectively)

Question 20

Spinal Cord

Answer 20

The spinal cord connects the CNS to the PNS. It is made up of nerves that extend from the medulla oblongata to the early lumbar region, where the remaining exists in a bundled group known as the cauda equina.

Spinal cord is 40-50cm in length and 2cm at its widest in the mid-thoracic region

31 neural segments give rise to 31 pairs of spinal nerves
Regions ( Cervical-> Thoracic -> Lumbar-> Sacral -> Coccygeal nerves)

Nerves emerge from the vertebral column between adjacent vertebrae

Question 21

Sensory Division

Answer 21

The sensory division involves the afferent pathway in which sensory receptors in the PNS detects and transmits sensory information from the body and environment to the CNS
Detects:
- Somatosensory Senses - touch, pressure, pain, temperature
- Visceral Sense - organ movement, pressure internally
- Special Senses - vision, sight, taste, smell, balance

Question 22

Somatosensory System

Answer 22

Responsible for detecting and processing sensory information from the body.

Stimulus detected by sensory receptors e.g. thermoreceptors in the peripheral nerves of the skin. Sensory neurons detect and send signal to the somatosensory cortex in the parietal lobe.

This allows the body to perceive and then respond to the changes in its environment maintaining balance and coordination

Question 23

Visual System

Answer 23

Light enters the eye and reaches the retina. The retina contains photoreceptors which convert light energy into electrical signals which is transmitted to the optic nerve. The optic nerve then communicates the signal to the visual cortex within the occipital lobe to interpret what is seen.

Question 24

Motor Division

Answer 24

Motor division of the nervous system refers to the efferent pathway. Involves the transmission of signals from the CNS to muscles and glands e.g. hypothalamus, to respond to the stimulus, maintaining homeostasis.
Split into:
- Somatic
- Autonomic (Sympathetic, Parasympathetic, Enteric Nervous System)

Question 25

Somatic Nervous System

Answer 25

Responsible for controlling voluntary movement of the body's skeletal muscles. and enables actions such as walking, talking (breathing when intentional), typing. Motor commands originate from the motor cortex in the frontal lobe and are transmitted down the spinal cord to our muscles.

Question 25

Autonomic Nervous System

Answer 25

Responsible for regulating involuntary movement that is necessary for survival e.g. digestion, heart rate, glandular activity Split into: - Sympathetic - 'fight or flight' responds to stressful or emergency situations e.g. increased heart rate, pupil dilation, redirecting blood to muscles - Parasympathetic: 'rest and digest' system, to promote relaxation and recovery especially after stress e.g. stimulating digestion, conserving energy, reduced heart rate - Enteric Nervous System: A complex network of neurons responsible for guiding gastrointestinal function (apart of parasympathetic kinda) e.g. hormone release, enzyme activity

Question 25

Neural Communication

Answer 25

Neurons are capable of transmitting information in the form of electrical signals called action potentials Action potentials can travel over relatively long distances (up to 1m in length) Axon endings will interact with another cell type (neuron, muscle cell etc. - if afferent or efferent) and form a synapse to transfer this information to the next cell

Question 26

Axon Hillock

Answer 26

Axon hillock is the conical-shaped junction where the axon joins the cell body Initial segment is thick unmyelinated section of the axon that joins the cell body at the axon hillock and is the site of action potential generation.

Question 27

Propagation of Action Potential

Answer 27

- **Action potentials** can **propagate along an axon in 2 ways** depending on the presence or absence of a myelin sheath around the axon 1. Contiguous conduction (unmyelinated axon) = slower 2. Saltatory conduction (myelinated axon) = faster

Question 27

Myelin Sheath (CNS & PNS)

Answer 27

CNS - Oligodendrocytes, one of them makes up many myelin sheathes PNS - Schwann cells, one of them makes up one myelin sheath Myelin is primarily composed of lipids, which are poor conductors of electricity. This means myelin sheaths acts as an insulator, similar to the plastic sheath around an electrical cable There are gaps in the myelin sheath called Nodes of Ranvier, where the action potential can regenerate.

Question 28

Juxtracrine Signalling

Answer 28

Membrane-bound proteins interact with other membrane proteins on adjacent cells Membrane-bound proteins interact with ligands in the extracellular matrix of adjacent cells. Signals travel via hydrophilic membrane channels/pores (gap junctions) between cells.

Question 29

Paracrine System

Answer 29

Local communication between cells that are in close proximity Chemical signal (neurotransmitters) released by one cell diffuse through the extracellular space to contact adjacent cells

Question 30

Autocrine Signalling

Answer 30

Chemical signals released by a cell bind to receptors on the same cell

Question 31

Endocrine Signalling

Answer 31

Chemical signals released by endocrine cells into the circulatory system to communicate with distant target organs

Question 32

Synapses

Answer 32

A synapse is a specialised junction between two neurons and an effector organ (muscle or gland). The most common type is the chemical synapse General structure of a chemical synapse Presynaptic cell Synaptic cleft Postsynaptic cell A form of paracrine signalling

Question 33

Presynaptic Cell

Answer 33

- Axon terminal containing synaptic vesicles - Synaptic vesicles containing neurotransmitter molecules - Voltage-gated Ca^2+ ion channels - Neurotransmitter re-uptake molecules (integral transmembrane, Na+/neurotransmitter symporter)

Question 34

Synaptic Cleft

Answer 34

Gap (~20-30nm) between the presynaptic and postsynaptic neuron

Question 35

Postsynaptic Cell

Answer 35

Receptor (signalling) Enzyme (neurotransmitter degradation) Within the postsynaptic neuron will be synaptic vesicles containing neurotransmitter Neurotransmitters are chemical messengers that neurons use to communicate with other neurons and cells. Neurotransmitters diffuse across the synaptic cleft and bind to receptors on the post synaptic cell.

Question 36

Chemical Synapses: Steps

Answer 36

Action potential arrives at nerve terminal Triggers calcium (Ca2+) to enter the presynaptic cell Ca2+ triggers exocytosis of neurotransmitter Neurotransmitter diffuses across synaptic cleft and binds to receptors on postsynaptic cell Response triggered in postsynaptic cell Response terminated by removing neurotransmitter from synaptic cleft

Question 37

Neurotransmitter If

Answer 37

Chemical messengers that carry signals across a chemical synapse from a neuron to post-synaptic neurons, muscle cells or other effector cells (e.g. glands) Criteria that define a substance as a neurotransmitter: Substance present in (and usually synthesised within) the presynaptic neuron Substance is released in a regulated fashion (usually exocytosis from synaptic vesicle) following stimulation of the pre-synaptic neuron Receptors for the substance must be present on the post-synaptic target cell Mechanisms must be present to remove or inactivate the substance

Question 38

Drugs Affecting Synapses

Answer 38

Drugs (exogenous ligands) have a similar chemical structure to the endogenous neurotransmitter Agonist: Substance that is similar enough to the endogenous neurotransmitter that it binds to receptors on the pre/post-synaptic membrane and activates them, e.g. morphine & heroin (opiates) mimic the effect of natural endorphins Antagonists: Substance that is similar enough to the neurotransmitter that it binds to the receptor site and blocks it, but not similar enough to activate the receptor e.g. curare binds to and blocks receptors on our muscles, causing muscle paralysis

Question 39

Neurodegneration