Week 3 Bioscience Flashcards
Functions of the Nervous System
- Sensory function
- receptors detect sensory input
- sensory input is sent to control centre
- Integrative function
- analyses & interprets sensory input
- determines appropriate responses
- generates the motor output that causes the response
- Motor function - issues motor output to activate an effector
General sensory receptors
· Are located in the skin, skeletal muscles, tendons, joints & visceral organs and include:
- thermoreceptors - detect changes in temperature
- nociceptors - detect painful stimuli
- mechanoreceptors
▪ tactile receptors - detect touch, pressure & vibration stimuli
▪ baroreceptors - detect changes in blood pressure
proprioceptors - detect changes in body position (proprioception)
Special sensory receptors
· Are located in the eyes, ears, mouth & nose and include:
- photoreceptors - detect light (vision)
- chemoreceptors - detect chemicals in solution (taste & smell)
- mechanoreceptors called hair cells - detect hearing & balance stimuli
CNS
· Consists of the brain and spinal cord
· Control centre - performs the function of integration
· Controls our emotions, behaviours and personality
· Performs intellectual (cognitive) functions § Stores memories
PNS
· Consists of sensory receptors and the cranial, spinal and peripheral nerves that link all parts of the body to the CNS
- cranial nerves and their branches primarily innervate structures of the head & neck
- spinal nerves branch to form the peripheral nerves that innervate all parts of the body below the head
Somatic Nervous System
· Conveys “somatic” motor output from the CNS to the body’s skeletal muscles
· Somatic motor output controls:
- voluntary skeletal muscle movements
- involuntary skeletal muscle movements = somatic reflexes
Autonomic Nervous System
· Conveys “autonomic” motor output from the CNS to the body’s glands, cardiac & smooth muscles
· Autonomic motor output controls involuntary (automatic) activities, e.g.
- heart rate
- respiration (respiratory airflow)
- blood vessel and pupil diameter
- digestion of food
- urination & defecation
- perspiration & salivation
Sympathetic division
Controls “fight-or-flight” activities - activates body functions that support physical activity and inhibits those that don’t, e.g.
- increases heart rate, respiratory airflow, blood flow to skeletal muscles & sweat gland activity
- dilates pupils
- inhibits digestive functions
- inhibits urination & defecation
Parasympathetic division
Controls “rest and digest” activities - activates body functions that conserve and restore body energy, e.g.
- stimulates digestive functions, urination & defecation
- constricts pupils
- decreases heart rate
- decreases respiratory airflow
Neuroglia (“nerve glue”)
- Support neuron development and function
- Six different types of cells which collectively nourish, protect, insulate and structurally support neurons
Neurons
· Specialised cells - perform the function of communication
- when stimulated they generate electrical signals called graded potentials and action potentials to conduct sensory and motor information from one part of the body to another
· Require oxygen and glucose for survival
- Are unable to divide and replace themselves if destroyed
dendrites
- Short processes
- Are the main receptive (or input) region of a neuron
- act as sensory receptors - detect stimuli
- receive information from other neurons
- Convert the information they receive into a graded potential which conveys the information towards the cell body
cell body
- Contains a nucleus and organelles, e.g., ribosomes to synthesise chemical neurotransmitters
- Receives information from other neurons & converts this information into a graded potential
- Integrates information (graded potentials) and conveys information towards the initial segment (or first part) of the axon
axon
- A single process that connects to the cell body at the axon hillock
- Is the conducting region of a neuron
- generates & conducts action potentials to convey information from the initial segment to the axon terminals
axon terminal
- Form a synapse with another cell - i.e. a neuron, muscle or gland
- Are the secretory region of a neuron
- contain synaptic vesicles that store and release neurotransmitters - chemicals that carry the information from one neuron to another or to a muscle cell or gland
myelin
- produced by Schwann cells and oligodendrocytes
- increases the speed of signal conduction
- segments are separated by gaps called nodes of Ranvier (internodes)
- destruction of myelin (oligodendrocytes) in the CNS - multiple sclerosis
Sensory Neurons
- Conduct sensory input from receptors to the CNS
- Unipolar in structure
Interneurons
- Conduct information within the CNS
- Multipolar in structure
Motor Neurons
- Conduct motor output away from the CNS to a muscle or gland
- lower motor neurons conduct somatic motor output
- preganglionic & postganglionic neurons conduct autonomic motor output
- Multipolar in structure
Chemically-gated Channels
- Open in response to a chemical stimulus e.g. neurotransmitters
- Located along the plasma membrane of the dendrites & cell body
Voltage-gated Channels
- Open and close in response to voltage changes (i.e. changes in membrane potential)
- Located along the plasma membrane of the axon and axon terminals
Mechanically-gated Channels
- Open in response to mechanical stimulation e.g. touch, vibration and pressure
- Located along the plasma membrane of the dendrites
Changes in membrane potential (voltage)
- Occur when a stimulus opens Na+ or K+ gated channels
- Are relative to the resting membrane potential = -70 mV
- Are described by terms depolarisation & hyperpolarisation
Depolarisation = membrane potential becomes less negative
When a stimulus opens Na+ gated channels:
- influx of Na+ ions into the ICF
- ICF gains +ve ions à cell interior becomes less negative
- membrane potential becomes less negative e.g. -70 mV to -60 mV
Hyperpolarisation = membrane potential becomes more negative
When a stimulus opens K+ gated channels:
- efflux of K+ ions out of the ICF
- ICF looses +ve ions à cell interior becomes more negative
- membrane potential becomes more negative e.g. -70 mV to -80 mV
Graded Potentials (GP)
- Are small changes in the membrane potential (i.e., a small depolarisation or hyperpolarisation)
- Originate in the dendrites or cell body of a neuron, when a stimulus opens chemically-gated or mechanically-gated channels
- Are short distance signals
- distance travelled is proportional to stimulus strength
stronger stimulus = bigger change in membrane potential = further signal will travel
Action Potentials (AP)
- Are long distance signals
- Originate at the initial segment of an axon
- Involve voltage-gated channels
- Are self-propagating
Chemical Synapse
- A junction that mediates the transfer of information
- At a chemical synapse between two neurons:
- the neuron sending the information = presynaptic neuron
- the neuron receiving the information = postsynaptic neuron
- presynaptic and postsynaptic membranes are separated by a synaptic cleft
- signal transmission involves chemical neurotransmitters
Termination of Synaptic Transmission
- The neurotransmitter diffuses away from the synaptic cleft
- The neurotransmitter is degraded by enzymes present in the synaptic cleft
- The neurotransmitter re-enters the axon terminal and destroyed by enzymes or reused. This process is known as reuptake.
