PSYC211 L1-14 - Professor David Bilkey

What are the two major divisions of the nervous system?

The central nervous system (CNS) and the peripheral nervous system (PNS)

What the the CNS comprised of?

The brain and spinal cord

What is the function of the CNS?

Processes information, integrates sensory input, and coordinates responses

What is the function of the PNS?

Carries sensory information to the CNS and motor commands from the CNS to muscles and glands

What are the two divisions of the PNS?

The somatic nervous system (voluntary movement) and the autonomic nervous system (involuntary movement)

What is the somatic nervous system?

The portion that interacts with the external environment, responsible for voluntary movement, made up of efferent (output) and afferent (input) nerves

Afferent nerves

Transmit information inward from sensory receptors (e.g., skin, organs, joints) to the central nervous system (CNS) - input sensory nerves

Efferent nerves

Transmit instructions outward from the CNS to the effectors (muscles and glands), allowing the body to react or maintain homeostasis - output motor nerves

What is the autonomic nervous system?

The portion that regulates the bodies internal environment made up of efferent and afferent nerves

What are the two divisions of the autonomic efferent nerves?

The parasympathetic nervous system and the sympathetic nervous system

What is the sympathetic nervous system?

The part of the autonomic efferent nerves driving the "fight-or-flight" response to prepare you for danger e.g. increasing our heart rate or dilating our pupils

What the the parasympathetic nervous system?

The part of the autonomic efferent nerves directing the "rest-and-digest" state to conserve energy and promote recovery

Dorsal side

The back

Ventral side

The front

What is the direction of information through the spinal cord?

Through the dorsal horn to the ventral horn

What are the dorsal and ventral horns made up of?

Grey matter inside the spinal cord

How many spinal nerves are there?

31 pairs connecting through the spinal cord

What are the 1st quadrant spinal nerves?

Cervical nerves, C1-C8

What are the 2nd quadrant spinal nerves?

Thoracic nerves, T1-T12

What are the 3rd quadrant spinal nerves?

Lumbar nerves, L1-L5

What are the 4th quadrant spinal nerves?

Sacral nerves, S1-S5 and coccygeal

Where do cranial nerves originate?

The brain, mostly in the brainstem

What do cranial nerves control?

Sensory and motor functions of the head and neck (except the vagus nerve, which also reaches thoracic and abdominal organs)

What is the function of spinal nerves?

To carry sensory information to the spinal cord and motor information to the body

What are the main functions of the spinal cord?

To relay information between the brain and body and coordinate reflexes

What is a reflex?

A rapid, automatic response that does not require conscious brain involvement

What the structures make up the forebrain?

The cerebral cortex, thalamus, hypothalamus, basal ganglia, hippocampus and amygdala

What is the function of the cerebral cortex?

Higher cognitive functions including thinking, memory, language, and perception

What does the thalamus do?

Acts as the major sensory relay station to the cortex

What does the hypothalamus regulate?

Homeostasis including body temperature, hunger, thirst, hormones and circadian rhythms

What is the function of the hippocampus?

Formation of new memories

What is the function of the amygdala?

Emotion processing especially fear and emotional learning

What are the major external features of a typical neuron?

The cell body, dendrites, axon hillock, axon myelin, nodes of ranvier and synapses

What are dendrites?

A branched extension of a neuron that receives signals from other neurons and transmits those signals to the cell body

What are axons

The long projection of a neuron that conducts electrical impulses or action potentials away from the cell body to other neurons, muscles or glands

What are synapses?

Junctions of axons where chemical signals are transmitted

What is the membrane potential of neurons maintained by?

Ions that are pumped across the membrane

What is the charge of the inside of a neuron?

Negatively charged compared to the outside, about -70mV

What is the sodium-potassium pump?

A process that constantly uses energy (ATP) to actively pump 3 +ve sodium ions out of the neuron and 2 +ve potassium ions into the neuron per cycle

What does the sodium-potassium pump create?

An electrochemical gradient essential for maintaining the neuron's resting membrane potential

What are transient alterations in the membrane potential of neurons?

Temporary, short-lived fluctuations in the electrical voltage difference across a cell's plasma membrane, in excitable cells (like neurons and muscle cells), this involves shifting away from a stable resting state (typically around -70mV) to send signals or perform cellular work

What are the two categories of transient alterations in the membrane potential of neurons?

Action potentials and graded potentials

When are transient alterations in the membrane of neurons produced?

When ions are allowed to cross the membrane through an ion channel

What is depolarisation of membrane potentials?

The process where a cells membrane potential becomes less negative/more positive, it is the first step in generating an action potential as when stimulated, voltage gated sodium channels open allowing positively charged sodium ions to rush into the cell

What is a graded potential?

A localised, short lived change in a neurons membrane potential in dendrites and the bof a neuron thats size is proportional to the strength of the stimulus and decays as it travels, can depolarise the cell to make it fire or hyperpolarise it to prevent firing, undergoes spatial and temporal summation

What is an EPSP?

An Excitatory Postsynaptic Potential that is a depolarisation bringing the membrane potential closer to the action potential threshold

What is an IPSP?

An Inhibitory Postsynaptic Potential that is a hyperpolarisation pushing the membrane potential further away from the threshold

What is an action potential?

An all or nothing pulse in axons depending on whether it reaches a threshold level of intensity at the axon hillock involving repolarisation and depdendent on volatage-gated channels

During depolarisation, which ion enters the neuron?

Sodium (+ve)

During repolarisation, which ion leaves the neuron?

Potassium (+ve)

Why do ions move through channels?

They move down their electrochemical gradient

What maintains the resting membrane potential?

The sodium-potassium pump (Na⁺/K⁺ ATPase)

What happens first in the Hodgkin-Huxley cycle?

The neuron is at resting potential (-70mV)

What happens during depolarisation?

Voltage-gated sodium channels open → Na⁺ enters the neuron

What happens at the peak of the action potential?

Na⁺ channels inactivate and K⁺ channels open

What happens during repolarisation?

K⁺ leaves the cell, making the membrane more negative

What causes hyperpolarisation?

K⁺ channels close slowly, allowing excess K⁺ to leave

How does the neuron return to resting potential?

Voltage-gated channels close and the Na⁺/K⁺ pump restores ion gradients

How does an action potential travel down an axon?

Depolarisation at one section opens voltage-gated Na⁺ channels in the next section

Why does an action potential only travel forward?

The previous section is in its refractory period

What is the absolute refractory period?

Na⁺ channels are inactivated; another action potential cannot occur

What is the relative refractory period?

A stronger-than-normal stimulus is needed to trigger another action potential

What is myelin?

A fatty insulating layer surrounding many axons

Which cells make myelin?

Oligodendrocytes in the CNS and Schwann cells in the PNS

What are Nodes of Ranvier?

Small gaps in the myelin sheath where voltage-gated ion channels are concentrated

What is the purpose of myelin?

To speed up action potential propagation

What disease is a result of demyelination?

Multiple Sclerosis due to a damaged myelin sheath causing numbness or weakness in one or more limbs, impaired vision, tingling and sensations and slurred speech