Wk 5: ANS Flashcards
ANS
component of the peripheral nervous system
Regulates involuntary physiologic processes
Hypothalamus
controls ANS and is responsible for basic survival strategies
Sympathetic origin of fibres
thoracolumbar region of spinal cord
Sympathetic length of fibres
Short preganglionic
Sympathetic location of ganglia
Close to spinal cord
Asympathetic origin of fibres
brain and sacral spinal cord
Asympathetic length of fibres
Long preganglionic
Asympathetic location of ganglia
In visceral effector organs
Sympathetic division functions
“Fight or Flight”
Promotes adjustments during exercise, or when threatened
- Increased heart rate
- Blood flow is shunted to muscles and heart
- Bronchioles dilate
- Liver releases glucose (from glycogen)
Parasympathetic division functions
Promotes maintenance activities and conserves body energy
After eating:
- ↓ blood pressure, heart rate deceleration, ↓ respiration rate
- Gastrointestinal tract activity is high
Sympathetic tone
keeps the blood vessels in a continual state of partial constriction
Special cases for SNS
- Innervation of adrenal gland (one ganglionic neuron)
- Innervation of sweat glands (release of Ach by post ganglionic neuron acting on muscarinic receptors in sweat glands)
Reflex
involuntary, fast and automatic response to a specific sensory stimulus
Areflexia
absence of reflexes
Hyperreflexia
Increased or overactive reflexes
Hyporeflexia
Decreased reflexes
Reflexes can be
Innate
Visceral
Spinal
Mono
Innate reflexes
neural reflexes, formed before birth and can disappeared with age
Grasp reflex (innate)
grabbing object if object touch palm
Moro reflex (innate)
protective motor response against abrupt disruption of body balance
Visceral reflexes
- Autonomic (e.g. control of heart rate)
- Or somatic reflexes (e.g. stretch such as patellar reflex)
Spinal reflexes
the spinal cord is the integration centre
- Cranial reflexes where the brain is only the integration centre (e.g. pupillary reflex)
Mono reflexes
one synapse involved (e.g. patellar reflex)
- Or poly-synaptic: such as the crossed extensor reflex or withdrawal reflex.
Components of a reflex arc
Sensory receptor
Motor neuron
Effector
Integrating centre
Sensory neuron
Sensory receptor
activated in response to stimulus
Motor neuron
neuron conducting impulses from integrating centre to effector
Effector
muscle or gland that responds to motor nerve impulses
Integrating centre
1+ regions within the CNS that relay impulse from sensory to motor neurons
Sensory neuron
conduct impulses from receptor to integrating centre
Somatic spinal reflexes are important reflexes since they can
- Contribute to posture and muscle tone
- Lead to adjustment of muscle tone dependent on task
- Compensate large disturbances
Types of spinal reflexes
Stretch
Tendon
Flexor or withdrawal reflex
Crossed extensor reflex
Flexor or withdrawal reflex (spinal reflex)
when pain receptors (nociceptors) are activated it causes automatic withdrawal of the threatened body part
Crossed extensor reflex (spinal reflex)
complex reflex consisting of an ipsilateral withdrawal reflex and a contralateral extensor reflex
Stretch (spinal reflex)
usually monitor muscle length
- Sensory receptors (muscled spindles) activate when a muscle is stretched
Tendon (spinal reflex)
monitors external tension produced during muscular contraction to prevent tendon damage.
- Controls muscle tension by causing muscle relaxation
- Receptor (golgi tendon organ) is in the tendon of the muscle
- Activated by stretching of tendon
Ageing effects on nervous system
- Rapid decline in brain weight
- Reduced bulk of gyri and widening of sulci
- Reduction of synaptic connections and neurons
- Reduced biochemical activity
The signs of NS ageing can be
- Altered sleep patterns
- Changes in mood, irritability
- Loss of appetite, constipation
- Loss of memory
