Senses and perceptions 2 Flashcards
What are the components of a sensory pathway?
receptor endings, peripheral nerve, ascending sensory pathway, cortical representation
What axons are found in a peripheral nerve?
axons from sensory and motor neurons
What are sensory neurons known as?
afferents
What are motor neurons known as?
efferent
Where are the axon terminals of sensory neurones located?
in the CNS
Where are the cell bodies of motor neurones located?
in the CNS
What is a fascicle?
a bundle of neurones
What is the endoneurium?
loose vascular supporting tissue that surrounds each nerve fibre in the fascicle
What is the perineurium?
condensed collagenous tissue layer that surrounds each fascicle
What is the epineurium?
loose collagen tissue that binds fascicles together and condenses peripherally to form a sheath
Function of the epineurium
provides structural integrity and mechanical protection to the nerve
Why is the presence of blood vessels crucial within nerves?
AP conduction is metabolically demanding. Vasculature supplies oxygen and glucose and removes waste products
What are myelinated axons encased in?
a series of Schwann cells line the length of the axon, each having a wrapped coating of myelin insulating the axon
What are unmyelinated axons encased in?
Schwann cell cytoplasm but no wrapped coating of myelin
What are the 4 types of afferent axons?
Aa (A alpha), AB (A beta), Ad (A delta), C
Which axon types are myelinated?
Aa, AB, Ad
What axon type is unmyelinated?
C fibres
Which axon type has the largest diameter and thickest myelin sheath?
Aa (A alpha) - diameter 13-20um
Which axon type has the fastest conduction speed?
Aa - speed 80-120m/sec
Which axon type has a relatively large diameter and myelin sheath thickness?
AB (A beta) - diameter 6-12um
Which axon type has relatively fast conduction?
AB 35-75m/sec (not as fast as Aa)
Which type of myelinated axon has the smallest diameter and myelin sheath thickness?
Ad (A delta) 1-5um
Which myelinated axon has the slowest conduction speed?
Ad 5-30 m/sec
Which axon type has the smallest diameter?
C fibres with a diameter 0.2-1.5 um
Which axon type has the slowest conduction speed?
C fibres 0.5-2 m/sec
Which sensory receptors are associated with Aa fibres?
proprioceptors of skeletal muscle
Which sensory receptors are associated with AB fibres?
mechanoreceptors of skin (innocuous tactile sensation e.g. pressure, brushing, touch)
Which sensory receptors are associated with Ad fibres?
nociceptors, thermoreceptors (pain and temp)
Which sensory receptors are associated with C fibres?
thermoreceptors, nociceptors, itch
What is the arrangement of white and grey matter in the spinal cord?
white matter surrounds the grey matter (central core)
What are the 3 sections the grey matter of the spinal cord is divided into?
dorsal horn (posterior), intermediate horn, ventral horn (anterior)
Where are the cell bodies of sensory neurones located?
dorsal root ganglia
How many dorsal root ganglia are there?
31 pairs (either side of vertebral column)
Describe the course of an action potential from a pin prick into the spinal cord
free nerve ending (nociceptors) of Ad and C fibres are activated. AP sent along sensory afferent, past dorsal root ganglia, into the dorsal horn
Describe the course of an AP from the spinal cord to skeletal muscle
motor efferent transmits the impulse from the cell body in the ventral root to the effector
What is a dermatome?
an area of skin supplied by a single spinal nerve
What does the dermatome map demonstrate?
demonstrates which segment of the spinal cord sensory input from distinct body regions project into
What is a myotome?
A group of muscles innervated by a single spinal nerve
What does the myotome map demonstrate?
the motor output controlled by segments of the spinal cord
What are the branches of the trigeminal nerve (CN V)?
ophthalmic (CN Va), maxillary (CN Vb) and mandibular (CN Vc) branch
Function of ophthalmic branch of the trigeminal nerve (CN Va)
sensory innervation of the scalp, forehead, dorsum of nose, upper eyelid, ethmoid, sphenoid and frontal sinuses
Function of the maxillary branch of the trigeminal nerve (CN Vb)
sensory innervation to lower eyelid, cheeks, maxillary sinus, lateral nose, upper lip, gingiva and teeth and superior palate
Function of the mandibular branch of the trigeminal nerve (CN Vc)
mixed sensory and motor. Sensory innervation to the chin, lower lip, teeth and gingiva, anterior 2/3 of tongue. Motor axons to the muscles of mastication
What are the muscles of mastication?
temporalis, masseter, medial and lateral pterygoids
How are the neural pathways in the CNS divided?
mechanoreception (touch) and nociception (pain) have separate pathways with the trigeminal nerve (face innervation) and spinal nerves (rest of body) considered separately.
