Spinal Cord/Nerves Flashcards
Where do free nerve endings occur?
Subcutaneous tissue and dermis
What are the two types of efferent neurons?
Somatic - skeletal muscle
Visceral - smooth muscle, cardiac muscle, secretory cells
Define peritichial nerve endings
Cage like formations of axons that surround hair follicles
Define Merkel cells and Merkel endings
Merkel cell - indented nucleus and electron dense cytoplasmic granules. Found in glabrous skin and in outer root sheaths of hair
Merkel endings - found in the germinal layer ( striatum basale ) of the epidermis
Define exteroceptive endings and proprioceptive endings
Exteroceptive endings - superficially located, such as skin, and responds to pain, temperature, touch and pressure
Proprioceptive - muscles, tendons and joints provide data for reflex adjustments of muscle action and for awareness of position and movement
Explain the difference between nonencapsulated endings and encapsulated endings
Nonencapsulated - terminal branches of the axon that may either be closely applied to cells or lie freely in the extracellular spaces of connective tissue
Encapsulated- distinctive arrangements of nonneuronal cels that completely enclose the terminal parts of the axon
Where are the following located:
1. Subcutaneous plexus
2. Dermal plexus
3. Papillary plexus
- Loose connective tissue deep in skin
- Densely collagenous reticular layer that constitutes the deeper part of dermis
- Papillary layer of dermis
Define:
1. Ruffini ending
2. Pacinian corpuscle
- An array of terminal branches of a myelinated axon surrounded by capsular cells
- A single axon that loses its myelin sheath and is encapsulated by several layers of flattened cells with greatly attenuated cytoplasm
Both found in subcutaneous tissue and dermis of both hairy and glabrous skin
Define Meissner’s tactile corpuscle
Occur in large numbers in the dermal papillary ridges of the fingertips
Supplied by three or four myelinated axons whose terminal branches form a complicated knot that is enclosed in a cellular and collagenous capsule
State the 5 modalities for skin
- Fine touch
- Vibration
- Light touch
- Temperature
- Pain
Define low threshold mechanoreceptors
Receptors for tactile sensation
Includes all encapsulated and some free nerve endings
What are nociceptors and what are the three types?
Receptors for painful sensations received by free nerve endings
- High threshold mechanoreceptors - mechanical stimuli
- Polymodal nociceptors - respond to mechanical and thermal stimuli and chemical mediators released from injured cells
- Hyperalgesia - chemical mediators
What is an receptor adaption?
A reduced response to continued stimulation.
Provide examples of slow and rapid adapting receptors
Rapid
1. Meissner’s corpuscles are sensitive to mechanical deformation allowing for the accurate detection of objects touching or moving across skin
2. Pacinian corpuscles are sensitive to vibration of fluid movement. Fastest to initiate a action potential.
Slow
1. Merkel endings respond to steady indentation of the skin.
What are the proprioceptive organs in skeletal muscles?
Neuromuscular spindles
Where are neuromuscular spindles generally located?
Near tendinous insertions of muscle.
Muscles that perform highly skilled movements e.g. hands
What does each neuromuscular spindle consist of?
Capsule of connective tissue with 2 to 14 intrafusal muscle fibres and extrafusal muscle fibres that surrounds the capsule
What sensory axons supply the neuromuscular spindle?
- Ia fibre (primary) - loses myelin sheath as it enters the capsule and the winds spirally around the miportions of the intrafusal muscle fibres in the form of an annulospiral ending.
- II fibre (secondary) - branches terminally and ends as varcosities on the intrafusal muscle fibre some distance from the mid region (flower spray endings)
What innervates the extrafusal fibres in neuromuscular spindles?
Alpha motor neuron (motor cells)
Gamma motor neurons (small motor cells) which supply the intrafusal muscle fibres within the spindle
What is the stretch reflex?
Slight stretching of a muscle lengthens the intrafusal fibres and the sensory endings are stimulated. Action potential are conducted to the spinal cord where the terminal branches of the sensory axons synapse with alpha motor neurons that supply the main mass of the muscle. The latter thereupon contracts in response to stretch through a two-neuron reflex arc. Stimulation of the spindles ceases when the muscle contracts because the spindle fibres, in parallel with the other muscle fibres, return to their original lengths.
What is the gamma reflex loop?
Consists of the gamma motor neuron, muscle spindle, sensory neuron, and alpha motor neuron supplying extrafusal muscle fibres.
What are Golgi tendon organs (aka neurotendinous spindles)?
Each receptor has a thin capsule of connective tissue that encloses a few collagenous fibres of the tendon. An Ib fibre brakes up into unmyelinated terminal branches after entering the spindle and branches end as varcosities on the intrafusal tendon fibres
How are Golgi tendon organs stimulated?
Tension
What surrounds synovial joints and what do they respond to?
Pacinian corpuscles
Respond to the cessation and initiation of movement
Which sensory ending does not have a Nonencapsulated terminal branches of axons?
Pacinian corpuscles
What are the two main components of the motor end plates?
- The ending of a motor axon
- The subjacent part of the muscle fibre
What is a motor unit?
Consist of one motor neuron and the muscle fibres that it innervates
Where does each branch of the motor nerve fibre give up its myelin sheath?
As it approaches a muscle fibre
What is the neurotransmitter in motor end plates?
Acetylcholine
What is the neurolemmal sheath?
Travels around the terminal branches of the motor axon
Why is the sarcolemma important?
Contains the enzyme Acetylcholinerase that inactivated acetylcholine.
Where does mitochondria accumulate in postganglionic autonomic endings?
Varicosities - swellings on the presynaptic effector nerve ending
What is the spinal ganglia?
Swellings on the dorsal roots of spinal nerves, just proximal to the union of dorsal and ventral roots.
What does spinal ganglia contain?
Cell bodies of primary sensory neurons, mainly in a large peripheral zone.
Centre is occupied by the proximal parts of the neurites
Are neurons in the sensory ganglia unipolar or bipolar?
Start as bipolar during embryonic stages but fuse together to become unipolar
Neurites in spinal ganglia are divided into what two branches and terminate at what location?
- Peripheral branch - terminates in a sensory ending
- Central branch - terminates in the spinal cord via a dorsal root.
What are autonomic ganglia?
Those of the sympathetic trunk along the sides of the vertebral bodies, collateral or prevertebral ganglia in plexuses of the thorax and abdomen, and certain ganglia near viscera.
What are the principal cells of the autonomic ganglia?
Multipolar neurons with the cell body surrounded by satellite cells.
What are peripheral nerves surrounded by?
Epineurium - composed of ordinary connective tissue and fills the spaces between the fascicles.
What is the prineurium
The sheath that encloses each small bundle of fibres in a nerve
Define endoneurium
Delicate connective tissue sheath surrounding an individual nerve fibre of a peripheral nerve.
Define epineurium
Connective tissue sheath surrounding a peripheral nerve.
What does a neuron fibre consist of?
The axon
Myelin sheath
Neurolemma
What are the nodes of Ranvier?
Interruption intervals in the myelin sheath
Define saltatory conduction
The rapid transmission of action potentials along a myelin sheath
How is the spinal cord protected?
Vertebrae and their ligaments
Meninges
CSF
What are the meningeal layers?
Dura matter
Subarachnoid
Pia matter
How is the spinal cord suspended?
Denticulate ligament on each side which is made up of Pia-arachnoid tissue. Attached to cord midway between the dorsal and ventral roots.
How many points is the denticulate ligament attached to the dural sheath
21 points between the foremen magnum and the level at which the dura is pierced by the roots of the first lumbar spinal nerve
Where is the epidural space located?
Between the dura and the wall of the spinal canal.
How many spinal nerves are there?
31
Each spinal nerve divides into a dorsal and a ventral what?
Primary ramus
What does the dorsal primary ramus supply?
The skin of the back and muscles that are attached to both ends to parts of the vertebral column.
What is the role of the central primary ramus?
Join, exchange fibres, and branch into the mixed nerves that carry motor and sensory axons to the skin and muscles of the lateral and ventral trunk and the limbs.
Where do the cervical spinal nerves exit the vertebral column?
Nerve C1 passes above the arch of vertebrae C1.
Nerves C2 - C7 go through foramina above the corresponding vertebrae
Nerve C8 passes through the foramen between the arches of vertebrae C7 and vertebrae T1
Where do the thoracic and lumbar spinal nerves exist the vertebrae column?
Nerves T1-L5 pass through foramina below the arches of the corresponding vertebrae
Where do the sacral and coccygeal spinal nerves exit the vertebral column?
Nerves S1-S4 branch into the primary rami within the sacrum, and the rami go through the dorsal and ventral sacral foramina
The fifth and the coccygeal nerves pass through the sacral hiatus.
Where are the dorsal root ganglia located?
Intervertebral foramina
Define caudal equina.
lumbosacral roots (longest roots) in the lower part of the subarachnoid space
Where is the spinal cord enlarged?
The cervical enlargement - includes segments C5 to T1
The lumbosacral enlargement - includes segments L2 to S3
What are the longitudinal furrows located on the surface of the spinal cord?
Ventral median fissure - contains connective tissue of the Pia mater and the anterior spinal artery and it’s branches
Dorsal median sulcus
What is in the gray matter of the spinal cord?
Dorsal and ventral horns and an intermediate zone.
A lateral horn, containing preganglionic sympathetic neurons, is added in the thoracic and upper lumbar segments.
What are the three main categories of neurons in the spinal grey matter?
- Motor cells of the ventral horn - supply skeletal musculature
- The cell bodies of tract cells - primarily located on the dorsal horn
- Interneurons - involved in local circuitry
What does the white matter consist of in the spinal cord?
Three funiculi:
1. Dorsal funiculus - consisting of gracile and cuneate fasciculus
2. Lateral funiculi (no anatomical demarcation)
3. Ventral funiculi (no anatomical demarcation)
Where does axon decussation occur in the spinal cord?
Ventral white commissure
What are some regional difference in the spinal cord?
- White matter increases in a caudal to ROSTRAL direction
- fibres are added to ascending tracts, and fibres leave descending tracts to terminate in the grey matter. - Grey matter increases in the cervical and lumbosacral enlargements for inner at ion of the upper and lower limbs
What is the laminae of Rexed?
Ten layers of neurons in the spinal cord
What is substantia gelatinosa?
Contains interneurons that have a prominent role in modifying the perception of pain
What are the distinctive columns of the motor neurons?
- Phrenic nucleus (C3-C5) for phrenic nerve - supplies diaphragm
- Accessory nucleus (C1-C5) for the accessory nerve
- Nucleus of Onuf (S2-S3) for inner at ion of the pelvic floor muscles
What are the distinctive cells columns in the thoracic and upper lumbar segments?
- Nucleus dorsalis - gives rise to the dorsal spino-cerebellar tract
- Intermediolateral cell column - consists of preganglionic sympathetic neurons
How many rootlets are branched from each dorsal root?
6-8 rootlets
Which tract do dorsal rootlets axons enter?
Lateral division
- Dorsolateral tract (of Lissauer)
Medial division (modalities of sensation other than pain and temperature)
- terminate in dorsal horn
What are some the long descending fibres of the dorsal funiculi?
- Septomarginal fasciculus
- Interfascicular fasciculus
Where do the majority of the ascending sensory fibres n the dorsal funiculus terminate?
Gracile and cuneate nuclei in the medulla
What two motor neurons are found in the ventral horn.
- Alpha motor neurons - supply the ordinary (extrafusal) fibres of striated skeletal muscles.
- Gamma motor neurons - supply the intrafusal fibres of the neuromuscular spindles (smaller and fewer)
What is the Renshaw cell?
A special type of interneurons that receives excitatory synaptic input from branches of the axons of nearby motor neurons. The branches axon of a Renshaw cell forms inhibitory synaptic junctions on motor neurons, including the same ones that are presynaptic to the Renshaw cell itself.
Focuses motor commands onto the muscles supplied by the most frequently firing motor neurons
What does each funiculi contain?
Ascending and descending fibres
What is the most important component of each dorsal funiculus?
A large body of ascending axons derived from neurons located in the dorsal root ganglia.
Concerned with the discriminative qualities of sensations, including the ability to recognise changes in the positions of tactile stimuli applied to the skin and conscious awareness of movement and of the positions of joints.
Where are axons added to each dorsal funiculus?
As the spinal cord is ascended, axons are added to the lateral side of each dorsal funiculus.
What is the lateral corticospinal tract consist of?
Axons of neurons in the cortex of the frontal and parietal lobes of the contra lateral cerebral hemisphere
Describe the lateral corticospinal tract pathway
Internal capsule - basis pedunculi of the midbrain - pons - medullary pyramids - decussation into the lateral funiculus of the cord
Where do the corticospinal fibres terminate if they are from:
1. Frontal cortex
2. Parietal lobe
- Intermediate grey matter of the ventral horn
- Dorsal horn
What is the raphespinal tract?
Unmyelinated fibres that contain serotonin. Produce painful sensations
What are hypothalamospinal fibres?
Unmyelinated fibres that may contain the peptide oxytocin
What is the largest body of ascending fibres in the dorsal part of the lateral funiculus?
Dorsal spinocerebellar tract
What is the largest tract in the ventral half of the lateral funiculus and what does it control?
Spinothalamic tract which conducts impulses concerned with tactile, thermal and painful sensations
Name the five tracts present in the ventral half of the lateral funiculus
- Spinothalamic tract
- Ventral spinocerebellar tract
- Spinotectal tract (aka spinomesencephalic tract)
- Spinoreticular tract
- Spino-olivary tract
What is the flexor reflex?
The withdrawal of a limb in response to a painful stimulus.
What is the function of the dorsal funiculus?
Adapted for the purpose of discriminative qualities of sensation
Name the two halves of the lateral funiculus
Dorsolateral fasciculus
Ventrolateral fasciculus
What is the function of the lateral corticospinal tract?
Concerned mainly with skilled volitional movement
What is the function of the raphespinal tract?
Modifies the transmission from the dorsal horn of impulses initiated by noxious stimuli, which produce painful sensations
What is the function of the unmyelinated hypothalamospinal fibres?
Contain oxytocin necessary for uterine contraction during birth
What is the function of the dorsal spinocerebellar tract?
Conveys proprioceptive information
What is the function of the spinothalamic tract?
Conducts impulses concerned with tactile, thermal and painful sensations.
What is the function of the ventral spinocerebellar tract?
Conveys sensory information from one lower limb to the same side of the cerebellum
What is the function of the spinotectal tract?
Concerned with spinovisual reflex
What is the function of the spinoreticular tract.
Perception of pain and of various sensations that originate in internal organs
What is the function of the ventral corticospinal tract?
Innervates muscles involved in fine control of the limbs
What is the function of the vestibule spinal tract?
Mediate equilibratory reflexes
What is the function of the reticulospinal tract?
Directs and controls the activity of motor neurons
