CH2 Nervous System Functioning Flashcards
Central Nervous System (CNS)
- Three main roles: to receive sensory information from the body, to send motor information to the body, to process information.
- Carries messages to and from PNS.
- Made up of the brain and spinal cord
The brain
- Is an intricate network of cells that processes information received through neural pathways from the body and directs/coordinates actions within the body.
A neural pathway comprises one or more circuits of interconnected neurons that form a communication network.
The spinal cord and its roles
- Is a cable-like bundle of nerve fibres that extends from the base of the brain to the lower back.
- Has two main roles:
- To receive sensory information from the body via the PNS and send these messages to the brain for processing.
- To receive motor information from the brain and send it to relevant parts of the body via the PNS to control muscles, glands and internal organs so that appropriate actions can be taken.
The Spinal Reflex
- Is an unconscious, automatic response controlled solely by neural circuits in the spinal cord; bypasses the brain
Why is the spinal reflex considered adaptive?
Something is considered to be adaptive when it assists in the sruvival of the organism. An immediate withdrawal response initiated by the spinal cord enables a faster reaction time (i.e. a fraction of a second before the sensory information reaches the brain). Thus, it allows an organism to save time while evading a possibly harmful situation.
Peripheral Nervous System (PNS)
- A system comprised of muscles, organs and glands
- Subdivisions: autonomic NS and somatic NS
- Has two main roles
- Receive motor information from the CNS
- Send sensory information to the CNS
6 steps in the spinal reflex
- Receptor cells within the skin of your feet detect a sharp poke from a pin left on the ground. A neural message is sent to a sensory neuron.
- Sensory neurons carry the message along a sensory, afferent pathway to the spinal cord.
- Interneurons relay the message to motor neurons
- Motor neurons carry the message along a motor, efferent pathway to the leg muscle, causing a withdrawal reflex (whereby the foot withdraws from the pin).
- Simultaneously, the message is carried up the spinal cord to the brain.
- The message is received in the brain (specifically in the area that processes this type of sensory information). Pain is consciously interpreted in the foot.
The Somatic NS
- Is responsible for initiating skeletal muscle movement
- Controls voluntary, goal-directed movements.
- Sensory information is received at sensory receptor sites in the body (skin, muscles, joints and tendons) and carried along sensory neural pathways by sensory neurons to the CNS.
- Motor information from the CNS is carried along motor neural pathways by motor neurons to skeletal muscles to control their activity by causing them to contract or relax.
Does NOT involve visceral muscles, organs or glands. Skeletal muscles are attached to our bones and respond to messages from the CNS to initiate, change or stop movement.
The Autonomic NS
- Regulates the activity of the visceral muscles (i.e. internal organs and glands).
- Connects the CNS to the body’s internal organs (e.g. the heart, stomach, liver etc.) and glands (such as sweat, salivary and adrenal glands), providing feedback to the brain about their activities.
- Primarily self-regulating (not entirely); without conscious awareness
- Split into three further sub-divisions: sympathetic NS, parasympathetic NS, enteric NS
Sympathetic NS
Activates muscles, organs and glands to prepare for action
Parasympathetic NS
- Maintains the body’s internal environment
- Counterbalances activity of the sympathetic nervous system
(Para)lysed; NOTE: The sympathetic NS and the parasympathetic NS are NOT at all separate from each other. Rather, one is dominant over the other at any given time depending on the situation.
Enteric NS
Dedicated to the functioning of the gastrointestinal tract
Structure of a neuron and the roles of each part
- Dendrites – convert neurotransmitters to action potential (i.e. receives neural information) and sends it to the soma
- Soma – processes info
- Axon – site of travelling action potential
- Myelin sheath – protects axon; speeds up action potential
- Axon terminal/terminal button – converts action potential into neurotransmitters before releasing the neural information into the synapse.
A neurotransmitter (Nt)
- Is a chemical substance released by a presynaptic neuron to send signals to the post-synaptic neuron.
- Its role is to transmit chemical signals to the adjacent neuron.
- Can be either:
- Excitatory – make postsynaptic neurons more likely to fire (i.e. release action potential)
- Inhibitory – make postsynaptic neurons less likely to fire
Neural information as electrochemical
- Communication between neurons may be electrical.
- E.g. axons transmit messages directly to other axons or directly to the cell body (soma) of other neurons; dendrites of one neuron communicate directly with the dendrites of other neurons via an electrical impulse.
- E.g. action potential.
- Communication can be chemical (i.e. neurotransmitters).
Excitatory v inhibitory neurotransmitters
- Excitatory – makes postsynaptic neurons more likely to fire (i.e. release action potential)
- Inhibitory – makes postsynaptic neurons less likely to fire
- Whether a neurotransmitter is excitatory or inhibitory depends on the properties of the receptor at the synapse, where it is released and on the receptor’s location in the brain.
The neural synapse
- Is the site where adjacent neurons communicate by transmitting neural signals to one another.
- Made up of the synapatic gap/cleft, the terminal buttons of the presynaptic neuron and the dendrites of the postsynaptic neuron
Neurohormones
- Are neurotransmitters that are also hormones.
- E.g. noradrenaline is secreted as a hormone by the adrenal glands into the blood, and as a neurotransmitter from neurons.
Glutamate (Glu)
- The main excitatory neurotransmitter in the CNS.
- Involved in normal brain function (i.e. learning, memory, perception, thinking and movement)
- Its excitatory effects promote the growth and strengthening of synaptic connections, subsequently improving memory of what as been learnt.
- Abnormally high concentrations of Glu can result in overexcitation of receiving neurons.
- Neuronal damage and/or death by overstimulating them.
Glu(cose) = gives energy; excitatory
Gamma-amino butyric acid (GABA)
- The main inhibitory neurotransmitter in the CNS.
- Fine-tunes neurotransmission in the brain and maintains neurotransmission at an optimal, or ‘best possible’, level.
- Low concentrations of GABA
- May cause seizures due to a lack of controlled activation
- Anxiety symptoms
A neuromodulator (Nm)
- Is a chemical (i.e. Nt) that is released by neurons to modulates, or influences, the effectiveness of other neurotransmitters.
- Altering neural transmission can be done by changing the reactivity of receptors to enhance their excitatory or inhibitory responses or controllling the synthesis + release of Nts.
A conscious response
- Involves awareness
- Is voluntary; intentional; goal-directed
- Exercises some degree of control
- e.g. speaking to a friend, picking up a water bottle
An unconscious response
- Does not involve awareness
- Involuntary; unintentional; automatic
- Is not typically controlled
- e.g. bodily responses regulated by the autonomic NS like digesting, blinking, breathing
Visceral muscles
- Are the muscles involved in the activity of internal organs and glands.
- Have built-in mechanisms for generating activity and do not depend on voluntary control from the brain.
- Are an important feature of the ANS → allows the ANS to function continuously - whether we are awake, active, asleep, under an anaesthetic or in a coma.