Chapter 11: Peripheral Nervous System Flashcards
what is peripheral nervous system
- includes all neural tissue outside the CNS
- provides communication between the CNS and the rest of the body
- has two divisions: efferent (motor) and afferent (sensory)
what are the parts of the efferent division?
1) autonomic nervous system
2) somatic nervous system
what is the autonomic nervous system?
- acts largely unconsciously to regulate involuntary processes including heart rate, blood pressure, respiration, digestion
- innervates most effector organs (i.e cardiac muscle, smooth muscle, glands)
- works with endocrine and behavioural state system to maintain homeostasis
two divisions of the autonomic nervous system
1) sympathetic nervous system = fight or flight
2) parasympathetic nervous system = rest and digest
what is the somatic nervous system?
- associated with the voluntary control of skeletal muscles and skin
what is the goal of the autonomic division?
- to ensure homeostasis is maintained
- one system always predominates depending on the state the body is in
at rest = the parasympathetic nervous system dominates.
body is excited or stressed = sympathetic nervous system dominates
describe the concept of dual innervation of the autonomic nervous system
- some effector organs are innervated by both divisions of the autonomic nervous system
- results in opposing antagonistic effects between the two autonomic divisions
- primary function is to help regulate organs and MAINTAIN HOMEOSTASIS
where does dual innervation not occur?
- sweat glands
- blood vessels
- adrenal medulla
what is the role of antagonistic control?
- necessary for homeostasis because it allows a physiological variable to either increase or decreases
- depends on dual innervation of a organ
- is used in autonomic branch of nervous system (one is excitatory and one is inhibitory)
- controls most internal organs
what does “fight or flight” mean?
- the sympathetic nervous system is most active during periods of excitation or physical activity
- the body prepares to cope with threatening situations
- heart rate increases, blood pressure increases, dilate pupils, energy stores are mobilized etc
what does “rest and digest” mean?
- the parasympathetic nervous system is most active during resting conditions
- both stimulates the digestive organs (digestion & absorption of nutrients) and inhibits the cardiovascular system (decreasing heart rate)
how does the autonomic nervous system maintain homeostasis?
- balances the activity levels of the parasympathetic and sympathetic nervous system
–> at low energy demands, heart doesn’t need to work hard because the body doesn’t demand blood = parasympathetic dominates
–> when body is active, energy demand increases and heart works harder = sympathetic dominates
how does the central nervous system regulate the autonomic nervous system?
- sensory information about the state of an organ or tissue is continuously relayed to homeostatic control centres in brain stem (hypothalamus, pons, medulla)
- the hypothalamus, pons and medulla act as an integrating centre. they take info and illicit a response
- the control centres tightly regulate bodily functions and regulate autonomic output (via sympathetic and parasympathetic systems) to maintain systemic homeostasis
- this means that heart rate, blood pressure, temperature etc are controlled and adjusted depending on the state of the body
what areas of the brain (CNS) regulate autonomic function?
- mainly the hypothalamus (known as “centre for homeostasis”), the pons and medulla
- these are called the integrating centre
anatomy of the autonomic nervous system
- consists of two efferent pathways containing 2 types of neurons (pre-ganglionic and post-ganglionic) that communicate between CNS and effector organs
- the neurons communicate via synapses in peripheral structures called autonomic ganglia
what is a visceral reflex?
- automatic changes in the functions of organs in response to changing conditions in the body
- the motor response of the body can be modified, facilitated, or inhibited by the CNS (hypothalamus, medulla, pons)
what is the concept of autonomic regulation (tone)?
- autonomic tone refers to the ongoing activity of the ANS when the body is at rest
- is the balance between sympathetic and parasympathetic activity
- tone can increase or decrease depending on the activity of the effector organ
what is the function of pre-ganglionic and post-ganglionic neurons?
- pre-ganglionic neurons travel from the CNS to the ganglia
- post-ganglionic neurons travel from the ganglia to the effector organs
–> usually a single pre-ganglionic neuron synapses with 8-9 post-ganglionic neurons
what is the autonomic ganglia?
- a cluster of synapses between pre-ganglionic and post-ganglionic neurons
- in each ganglion, there are axon terminals of pre-ganglionic neurons
- in each ganglion, there are cell bodies and dendrites of post-ganglionic neurons
how do sympathetic and parasympathetic neuron pathways differ?
1) the pathways point of origin within the CNS
2) location of the autonomic ganglia
in sympathetic division:
- most pathways originate in thoracic and lumbar regions of spinal cord
- ganglia is proximal to spinal cord
- short pre-ganglionic neurons that synapse with ganglia
- long post-ganglionic neurons that go to effector tissue
- stimulates tissue metabolism and alertness
in parasympathetic division:
- pathways originate in brain stem and leave via cranial nerves
- ganglia is proximal to effector/target organs
- long pre-ganglionic neurons to synapse with ganglia
- short post-ganglionic neurons to effector organs
- stimulates digestion and lowers HR
what is the role of the vagus nerve in the parasympathetic nervous system?
- about 75% of all parasympathetic neurons are running through the vagus nerve
- most parasympathetic innervation is to the head, neck and internal organs via the vagus nerve (originates in brain stem)
- sensory info comes from internal organs to brain and parasympathetic info goes brain to internal organs
what other nerves play a role in the parasympathetic nervous system?
- cranial nerve III (occulomotor)
- cranial nerve VII (facial)
- cranial nerve IX (glossopharyngeal)
- sacral spinal nerves
what are the 2 primary neurotransmitters in the peripheral nervous system?
- acetylcholine
- norepinephrine
what are neurons that releases neurotransmitters referred to as?
release acetylcholine = cholinergic
release norepinephrine = adrenergic
