Nervous Systems

the roles of different subdivisions of the central and peripheral nervous systems in responding to, processing and coordinating with sensory stimuli received by the body to enable conscious and unconscious responses including spinal reflexes

Central and Peripheral Nervous System

Central= brain and spinal cord

Peripheral= everything else (muscles, organs, glands)

• they both control the way we process and respond to information

Central Nervous System

Spinal cord= bundles of nerves encased by spine/ vertebrae and sends motor information to the P.N.S

Function: receives sensory information from the P.N.S (body)

• it sends this info through neurons

Brain: regulates and guides all parts of the nervous system

It is responsible for:

• vital body functions (breathing, heart rate, digestion etc.)

• Receives info from outside world via senses and coordinates a response

• high order functions like planning and thinking

• emotions, personalities, sense of humour

Process:

1. Receives sensory information and this info travels tp the brain through sensory neurons

2. Brain considers and process information linking it with other information

3. Brain coordinates a response to sensory information

Spinal cord: cable-like column of nerve fibres, extending from the base of the brain to the lower back

• it is like a 2 directional highway

• sends sensory/afferent messages toward the brain through afferent tracks

• it sends motor/efferent messages away from the brain through efferent tracks

• there are however, responses that don’t go all the way to the brain and are instead intercepted at the spinal cord

SAME:

Sensory → Afferent: conducting towards

Motor → Efferent: conducting away

PERIPHERAL NERVOUS SYSTEM:

Function: sends sensory info to C.N.S, receives motor info from C.N.S

• The two nervous systems work together to complete action

The peripheral nervous system is split into two parts:

Somatic: network of neurons within body that transmit information from receptors to the C.N.S, then carry motor info to the muscles, initiating voluntary movement

Autonomic: neurons that carry information between the C.N.S and the organs and glands to regulate them without conscious awareness

The autonomic nervous system is further broken down into the parasympathetic N.S and the sympathetic N.S

Sympathetic: prepares the body for action to deal with a potential threat, it activates the fight-flight-freeze

Parasympathetic: maintains homeostasis in body and returns the body to a state of calm after stress

Parasympathetic= parachute → brings you back down

Sympathetic N.S: activates internal muscles, organs and glands to prepare for rigorous activity or deal with a stressful situation

The S.N.S releases adrenaline (hormones) this increases energy and alertness, as it tells other organs to switch on, increases heart rate and respiration, liver releases glucose, dilates pupils for better vision, relaxes bladder

• if question asks for physiological changes, can’t say fight-flight response is activated, it’s not specific enough

*in order for this to happen other physiological functions are suppressed - inhibits digestion, hunger etc.

Parasympathetic N.S: keeps body functioning effectively, maintains homeostasis in times of low stress, it counter balances the sympathetic N.S, returning the body to a state of calm e.g heartbeat slows, bladder relaxes, pupils contract

• like a parachute, relaxes you back down

Fight-Flight-Freeze Response

• initiated by sympathetic N.S, preparing the body for action and to confront a stressful situation, optimising chances of survival

• some people will fight the stress, others will go into flight and run, some will freeze to go unnoticed (more commonly animals)

• all of these responses a are adaptive and provide different advantages

Enteric Nervous System:

• controls entire digestive tract from oesophagus to anus

• it does not require the brain

• sends messages via vagus nerve (which connects gut and brain)

Conscious and Unconscious Responses

Neurons are the building blocks of the nervous system

• neurons all look slightly different depending on their function

• they are the cells that transmit messages

• neurons do not move, messages travel through them

if a bright light is suddenly shone into your eyes you may raise your hand in front of your face to block the light (this is a conscious response of your somatic n.s)

however your pupils will also constrict automatically (this is an unconscious response of your autonomic n.s)

conscious response to stimuli:

• involves awareness and attention

• intentional and goal directed / have purpose

• can be learned and controlled

• can be complex and variable

*however sometimes we can break these roles and unconsciously act without the brain, spinal reflexes

unconscious response to stimuli:

• does not involve awareness or attention

• unintentional and reflexive

• often not learned and uncontrolled

• can be simple and constant

*however sometimes we can break these roles and consciously control these unconscious responses e.g keep eyes open to stop blinking

unconscious responses:

• not all responses performed by the somatic nervous system are conscious and voluntary

• some simple responses essential for survival occur automatically between the somatic ns and the spinal cord

spinal reflex:

• occurs in spinal cord and is independent of the brain, involves sensory, interneurons, motor neurons

• sensory information sent through somatic nervous system via afferent tracks to spinal cord, motor information

• sensory message goes to spinal cord, reaches interneuron which directly connects sensory response with motor response, without going all the way to the brain

• this initiates a movement in our skeletal muscles

advantages:

• help us automatically adapt to changing conditions

• allows quicker reaction times when confronted with hazards

• improves chances of survival by getting away from danger

• leaves the brain free to deal with other important things happening at the same time

Controlling autonomic responses:

• while the ANS is mostly self regulating and involuntary, there are times we can use techniques to control it e.g breathing, blinking

Sensory neuron: carries sensations/feelings towards brain

• transmit sensory info via afferent pathways from body to brain

Interneurons: talks between neurons and in the brain coordinating responses

• communicators that transmits info between sensory and motor neurons

• they are most abundant in the brain

• they are not found in the rest of the body/P.N.S

• only found in spinal cord and brain

Motor neurons: sends messages to body/P.N.S for response

• transmit motor information from brain to body via efferent pathways

Neural Communication

1. Sensory/afferent neurons at the receptor site (the skin) feel sensation

2. They pass info along afferent tracks through the PNS, to the spinal cord and eventually to the brain

3. Interneurons in the brain communicate with motor/efferent neurons

4. Motor neurons send info through efferent tracts in the spinal cord, then through the P.N.S and to an effector site (the muscle

Conscious vs. Unconscious Responses

• Spinal reflex is an automatic, unconscious response that is initiated by neurons in the spinal cord and DOES NOT INVOLVE THE BRAIN

• it is a response to pain- so that we can respond more quickly, optimises chances of survival

• The sensory info containing the “pain” is intercepted by interneurons in the spinal cord