The Nervous System - Chp 33

What is the nervous system divided into?

CNS - Central Nervous System

• brain + spinal cord

PNS - Peripheral Nervous System

• network of nerves that bring signals between the CNS and the rest of the body

Sensory Neuron Diagram

Where is the cell body of a sensory cell?

outside the CNS/ in the PNS

Motor Neuron Diagram

Where is the cell body of a motor cell?

in the CNS

Neuron

functional cells of the nervous system, that carry electrical signals to and from the CNS to bring about a response

Receptor

a cell or group of cells that detects a stimulus

Nerve endings

connect sensory neurons to receptor cells or sense organs

Dendrites

fibres that carry impulses towards the cell body of the neuron

Schwann cells

Resting Neuron

are neurons where no impulse is being carried

Threshold

an electrical impulse will only be carried along a neuron when it meets its threshold

All or Nothing Law

is the threshold is not reached there will be no impulse carried, and if the threshold is met the impulse will be carried

Describe the movement of an impulse through a neuron

• a resting neuron has a higher negative ion concentration inside, and a higher positive ion concentration outside

• when the threshold is met, the neuron changes its permeability to ions

• this allows positive ions to move into the neuron, and the concentration changes to positive on the inside and negative on the outside

• this happens section by section as the impulse travels down the neuron

What affects the speed of an impulse?

• the myelin sheath

  • if present - the impulse jumps from each node of ranvier to the next, making the impulse travel faster

  • if not present - the impulse will be a lot slower

• the larger the diameter of the neuron, the faster the impulse will be passed along

Synapse

the region where 2 neurons come into close contact with each other

Synaptic Cleft

the tiny gap between the 2 neurons

Neurotransmitter

convert electrical signals to chemical signals so they can cross over the cleft to the next neuron, where they are converted back into electrical signals

Name 2-3 neurotransmitters

• Acetylcholine

• Noradrenaline

• Dopamine

Synapse Diagram

How do neurotransmitters move from one neuron to another?

diffusion

What happen to the neurotransmitters after they cross the synaptic cleft?

• enzymes in the post-synaptic neuron digest the neurotransmitters

• they are moved back to the swellings in the pre-synaptic neuron and can be used again

What are the functions of the synapse?

• transports impulses from one neuron to the next

• controls the direction of the impulse

• prevents overstimulation - with constant stimulation over a long period of time neurotransmitter stop being produced

How do painkillers work?

they stop the impulse by blocking the neurotransmitters crossing a synapse

What is the function of the brain?

sorts all incoming impulses from sensory neurons + decides a response

What bones protect the brain + spinal fluid?

• skull

• spine

What does the brain consist of?

Grey matter - made up of cell bodies and synapses

White matter - made up of nerve fibres/axonz

What protects the brain inside the skull + spinal cord?

• 3 membranes called the meninges

• cerebrospinal fluid between the membranes + around the brain

What is the function of the cerebrospinal fluid?

• acts as a shock absorber

• is an exchange medium between the brain and the blood

Cerebrum - function

• controls voluntary muscles

• receives impulses from sense organs

• controls intelligence, memory + personality

Cerebellum - function

Controls muscular coordination and balance

Medulla - function

controls involuntary actions

Thalamus- function

sends messages to different parts of the brain

Hypothalamus - function

controls internal environment of the body

Disorder of the Nervous System - cause, symptoms + treatment

Parkinsons disease

• caused by a lack of dopamine in the brain

• trembling limbs, rigid body, inability to walk

• cannot be prevented, treatments include drugs + physiotherapy

Where is the spinal cord located?

in the neural canal

Draw + describe the structure of the spinal cord

• outer white ring made of white matter

• inner H shaped tissue made up of grey matter

• central canal contains cerebrospinal fluid

• the dorsal root carries sensory neurons to the spinal cord

• the ventral root carries motor neurons out of the spinal cord

Reflex action

an automatic response to a stimulus, they are fast and designed to protect the body from harm

What is the reflex arc?

if a message is sent to the spine and it is very strong, the response happens before the message has been received and processed in the brain

Examples of reflex actions

• grasp reflex in young children

• blinking the eyes

• breathing

• knee jerk

Diagram of a withdrawal reflex action

Describe the process of a withdrawal reflex

• receptors in the finger are stimulated by the hot flame

• sensory neurons carry impulse through the dorsal root to spinal cord

• in the spinal cord numerous synapses are made with other neurons

  • and interneuron carries the impulse to a motor neuron

  • another neuron takes the impulse to the brain

• motor neurons take the impulse through the ventral root to the effector

• at the same time that the hand withdraws, the impulse reaches the brain, this makes us aware of what happened and some pain, however, the actions was not caused by the brain