Lecture 2 - The Spinal Cord Flashcards
Where does the sensory cortex get an input from and what is that input called.
sensations from skin
to the sensory cortex in the brain
sensory input
How does a sensory input work?
sensations from the skin
31 nerve fibres go into spinal cord
spinal cord sends/conveys long nerve pathways up to the top of the spinal cord (the brain)
to the PRIMARY sensory cortex
Where are the spinal chord nerves placed?
between each of the bones of the vertebrae
What are the nerves coming out of the spinal cord called?
spinal nerves
each goes to an individual dermatome (band/region of skin)
How many spinal nerves are there?
31
(30 go to the skin)
vs only 30 dermatomes
How do you name spinal nerves?
1-8pairs= neck/cervical s.n. 9-20 (12x)pairs= thoracic s.n. 21-25 (5x)pairs= lumbar s.n. 26-30 (5x)pairs= sacral s.n. 31 (1x)pair= around anus/coccygeal s.n.
each goes to a region of skin/dermatome
What is a Dermatome?
a region/band of skin/body an individual spinal nerve goes to
30x dermatomes
nerve innervates skin at level of dermatome
dermatome provides sensory input to the CNS via the posterior roots of a pair of spinal nerves, or via the trigeminal (V) nerve
How does a Dermatome work?
provides sensory input to the CNS via
a. the posterior roots of a pair of spinal nerves
b. trigeminal (V) nerve
Describe the placement of the spinal cord
Extends from the medulla oblongata
To the superior part of the 2nd Lumbar Vertebrae
Terminates as a comical structure called the concus medullan’s
-between the 1st and 2nd lumbar
Nerve motorways
Sensory fibres which come in through the spinal nerve
too 2x roots
-upper=dorsal/posterior/afferent root, for information coming INTO the spinal cord from peripheral receptor, sensory
-lower=ventral/anterior/efferent root= for information LEAVING the spinal cord too skeletal muscles, motor
What is the Concus Medullans and describe its relevance
termination of the spinal cord
terminates as a somical structure called the Concus Medullan’s
between the 1st and 2nd lumbar vertebrae
therefore spinal nerves from the lumbar, sacral and coccygeal (pairs #21-31) respective regions’/dermatomes do not the leave the vertebral column at the same time they exit
roots called the Caudal Equine
What is the Caudal Equine and describe it’s relevance
Roots
spinal nerves 21-31 from the - Lumbar, Sacral and Coccygeal regions’ do not leave the vertebral column at the same time they exit (due to concus medullan’s/comical structure)
Which root has bulge?
dorsal/posterior root
bulge=dorsal root ganglion
What happens if the Dorsal/Posterior/Afferent root was cut?
There would be NO information coming INTO the spinal curve from that particular dermatome
the skin will be numb
What is the Dorsal Root?
Posterior/Afferent root
contains Only SENSORY nerves
“ON ramp”
conducts impulses from Sensory Receptors –> to CNS
What is the Ventral Root?
Anterior/Efferent root
contains Only MOTOR nerves
“OFF ramp”
conducts nerve impulses from CNS –> to Efferent Organs and Cells
What does Myelin cover?
Nerve fibres
What is Gray matter?
Dendrites&Cell Bodies of neurons
Unmyelinated axons and neuroglia
gray matter on each side of the spinal cord is divided into “horns”
is the inner core of the spinal cord
receives and integrates incoming/outgoing info
What is White matter?
primarily of bundles of Myelinated Axons of neurons
“motorways”
travel of SENSORY INputs and MOTOR OUTputs
What does the spinal cord consist of?
White matter(motorways) + Inner core of Gray matter
Why do you not count C1?
C1 doesnt go to the skin
-C1 takes the VENTRAL root not the dorsal root
What does a nerve consist of?
Cell body
2x Roots - Dorsal root + Ventral root
What are Dorsal Root Ganglian Cells?
Enlarged cell bodies which support dorsal nerve fibres
1x process out to skin +
1x process out to DORSAL HORN/spinal chord to convey information - 2x sets of sensory fibres into the brain
What is a Peripheral receptor?
Encapsulated receptor
Specialised receptor which forms a capsule around the end of nerve fibre “onion”
Discriminative Sensation-can discriminate in a precise way down to
What is the need for Myelin?
“Myelinated Nerve Fibre” formed by Schwann Cells wrapped around axons
Fast conducting fibre
Nerve impulses travel fast 50ms-1 b/w nodes.o.R.
Instantaneous information to brain
Saltatory transmission
What are fibres sensitive to touch called?
Meissner Corpsudes
convey discriminative information skin/dermatome–> spinal cord
What are fibres sensitive to pressure called?
Paciuian Corpsudes
convey discriminative information of pressure skin/dermatome–> spinal cord
What happens when you have a sensation?
you can feel it in its respective area in the sensory cortex on the other side of your brain
How is a spinal nerve organised?
highly organised
Sensory nerve
each spinal nerve contains 10,00 myelinated fibres from/per dermatome due to # of the spinal nerve
Describe LMN’s
Lower Motor Nerves
Off Ramps
Large Cells-120microns
In Ventral Root
these axons conveys motor info out to muscles from the motor cortex which have connected to the dendrite
Terminate on Muscle Cell
Synaptic junction when reaches Skeletal muscle,
acetylcholine release–> contraction
1000s on a single muscle cell
co-ordinated contraction of skeletal muscle
Peripheral Nerve
Essential
Damage: muscle wouldn’t receive impulses, becomes Paralysed/Floppy Meat- Flaccid Paralysis
Describe Pain and Temperature Fibres
Similar to spinal nerves but different in organisation
Convey sensations of Pain and Temperature
Non-encapsulated Receptor (nerve endings have no capsule around it)
Endings end in Dermis - Naked Nerve Endings
Free Nerve Endings
Sensitive to Pain Thresholds and changes in Temperature
Sensitive in a general way (smaller number of these pain and temperature fibres relative to touch and pressure fibres)
Non-discriminative Sensation- REGION- you can fell pain and temperature but you CANNOT LOCALISE it in a precise way as touch and pressure
Non-myelinated –> 1ms-1 as no nodes
ends at centrey part of spinal cord
Cell body in the Dorsal Root Ganglion Neuron
What are some comparisons between the two sets of fibres coming in from the skin?
Touch and Pressure
Discriminative sensations
Heavy Myelin covering
Information passes in a Saltatory Fashion - very fast rate 50ms - due to Nodes of Ranvier
Myelin formed by Schwann Cells
End of fibres have capsule around therefore Peripheral Receptor or Encapsulated Receptor
Function: to generate nerve impulse in a discriminative sensation
Terminate in BOTH Dorsal Horn and Brain (via branching fibre)
Thinner Non-myelinated fibres Temperature and pain fibres Conduct slower rate 1ms No receptor at end - Non-Encapsulated Receptor Naked/Free Nerve Ending Convey Non-discriminative Information Terminate in Dorsal Horn
What is present in the Dorsal Root Ganglion and what is a name for them?
PseudoUnipolar Neurons
both the Sensory Myelinated Fibres sensitive to touch and pressure and the Naked Non-Myelinated Pain and Temperature Fibres
What is the function of a Peripheral/Encapsulated Receptor?
Capsule is wrapped around like an onion
Function is to turn light touch or pressure to generate a nerve impulse and the termination of that fibre
makes the fibre VERY SENSITIVE
How do the two sets of nerve work in a dermatome?
First get touch and pressure
if pressure gets intense then you get pain which is conducted by other fibres
temperature and pain is felt in a general region
What are UMN?
Upper Motor Neurons
Control Movement
Start in Motor Cortex
Come down, Cross the Spinal Cord and have to get information out to Muscles under the Skin
What would happen if the Dorsal Root was cut?
Numbness
No sensory information- touch&pressure, pain&temperature
What would happen if the Ventral Root was cut?
Flaccid Paralysis-
Muscle doest receive nerve impulses
Floppy muscle
What is meant by the Peripheral Nerve?
Spinal Nerve branches Goes out to particular parts of the body Mixture of Sensory and Motor Nerves To either Skin(Dermatomes) or Muscle Combine to form Complex Systems
What is difference within the 31 Spinal Nerves?
30 Spinal Nerves go to one Dermatome (Dorsal Root)
31 Spinal Nerves go to Muscles (Ventral Root)
What happens if the Spinal Cord becomes compressed and cut?
become Paraplegic
Lower parts:
Paralysed (no muscle use)
Lose all sensation in Skin
