Unit 3 Flashcards
What is the spinal cord?
Part of the CNS within spinal column
Main pathway of communication between brain and body
Consists of spinal nerves
What are vertebrae?
The many bones the spinal column consists of
What is the main pathway between brain and head?
Cranial nerves
The relationship between reflex circuits and the spinal cord
Mainly make use of spinal cord with little input from brain
-> degree of autonomy of spinal cord
Structure of the spinal cord
Segmented
Each segment with one pair of spinal nerves (31 in total)
1 pair consists of a sensory and motor nerve on each side
Where do sensory nerves attach?
Attach on spinal cord in dorsal roots
Where do motor nerves depart from?
Depart from spinal cord in ventral roots
What happens if the spinal cord is cut?
Brain loses sensation + motor control from the cut segment and below
What does the pathway between spinal cord and Brain consist of?
Axon tracts
-> ascending and descending pathways
What is a polysynaptic reflex?
A reflex with an interneurone
-> relatively easy to inhibit
What is a monosynaptic reflex?
A reflex without interneurones
-> relatively hard to inhibit
How is the spinal cord protected?
Spinal/vertebral column
Meninges
CSF
How many individual vertebrae are in the spinal column?
24
What regions can you divide the spinal column into?
Cervical (neck)
Thoracic (chest)
Lumbar (lower back)
Sacral and coccygeal combined (pelvic region)
What is a spinal foramen?
A hole in the centre of each vertebra
-> allows the spinal cord to pass through
Pia mater
Innermost layer
Delicate membrane
Adheres to surface of spinal cord and spinal root
Dura mater
Outermost layer
Tough, durable, flexible and unstretchable membrane
Approximate diameter of the spinal cord
Little finger
-> although: diameter not uniform
What are the two enlargements of the spinal cord ?
Cervical enlargement: innervates upper limbs
Lumbar enlargement: innervates lower limbs
Pairs of spinal nerves
One spinal nerve on left and one on right side of the body
Consist of bundles of axons joining together or departing from spinal cord as dorsal or ventral roots
Dorsal + ventral root -> 1 spinal nerve
What does the dorsal root contain and where are its cell bodies?
Contains afferent neurones
-> carry sensory information from peripheries of body to brain
Cell bodies: dorsal root ganglia outside spinal cord
What do ventral roots contain and where are the cell bodies?
Contains efferent motor neurones
-> innervate skeletal muscles
Contain preganglionic neurones
-> control autonomic NS
Cell bodies within grey matter of spinal cord
How are spinal nerves mixed?
Contain sensory component from dorsal root and motor component from ventral root
Dermatome
A specific segment of the spinal cord receives stimulation from limited area of body (the different areas corresponding with spinal cord segments)
How does information of different parts of the body get to the spinal cord?
Stimulation detected by receptors in given dermatome
-> communication of message along corresponding spinal nerve to specific segment of spinal cord
Example for the way dermatomes work
Touch of shoulder will cause a sensory nerve to send neural impulse to cervical segment 4 (C4) of spinal cord
Are dermatomes perfectly distinct
No, they overlap to a degree with neighbouring dermatomes
-> if one spinal nerve is damaged, sensation may not be completely lost in corresponding area of the body
Central canal
Part of ventricular system
Allows flow of CSF
Grey and white matter in spinal cord
Grey matter internal
White matter external
Grey matter surrounds central canal forming butterfly stucture
The four protrusions of the spinal cord grey matter
2 dorsal horns
2 Ventral horns
In middle segment: lateral horns
Dorsal horn
Site at which sensory neurones (arriving via the dorsal root) terminate
What does the ventral horn contain?
Contains cell bodies of motor neurones (exiting the spinal cord at ventral roots and innervating effector organs)
Contains laminae important for movement
Lateral horn
Location of cell bodies of sympathetic preganglionic neurones
What can dorsal and ventral horns be divided into?
Laminae and nuclei
Laminae in the spinal cord
Known as Rexed‘s laminae
Numbered I-X
Run dorsally to ventrally
Dividing the cell bodies of the dorsal horn
Two types: most dorsal and more ventral parts
Most dorsal part of the dorsal horn: receives somatosensory information
More ventral part of the dorsal horn: receives visceral sensory information (i.e. sensory information regarding internal organs)
Lamina VII
Spans dorsal and ventral horns
More dorsal and lateral portion: site of sympathetic preganglionic neurones projecting from lateral horn in middle segments of spinal cord
Sacral segments: parasympathetic preganglionic neurones
Motor neurone disease
Affects motor neurones originating in ventral horn
Characterised by muscle weakness, low muscle control and muscle wasting
How is white matter in the spinal cord organised?
Into columns: dorsal, ventral and lateral columns
Ascending and descending tracts within columns
Ascending tracts
Carry different types of somatosensory information to different locations of the brain
Examples:
- spinothalamic tract: carry pain, temperature, coarse touch and pressure information
- fasciculus gracilis & fasciculus cuteanus: in dorsal column, carry impulses regarding proprioception and fine touch
When can ascending information reach consciousness?
When the destination is the cerebral cortex
When does ascending information not reach consciousness?
E.g. when destination is the cerebellum
What is the cerebellum responsible for?
Balance & posture
Contains purkinje cells
What do descending white matter tracts do?
Communicate information regarding movement, muscle tone
Influence spinal reflexes, autonomic functions and modulate ascending sensory information (enhance or reduce strength of signals sent to brain)
What can descending tracts be categorised into
Two groups:
1. Lateral column tracts
2. Ventromedial column tracts
Lateral column tracts
Lateral corticospinal & rubrospinal tracts
Control voluntary limb movements
Ventromedial column tracts
Ventral corticospinal, tectospinal, vestibulospinal and reticulospinal tracts
Control more automatic movements (e.g. reflexes and unconscious coordination of limbs for posture and balance)
Interneurones
Neurones whose entire cell is contained within a single structure
Important role in reflex movements
What is a reflexive motor response
Involuntary response triggered by a sensory stimulus (e.g. tapping just below knee and knee jerk reflex
Types:
- monosynaptic reflexes arcs
- polysynaptic reflex arcs
Monosynaptic reflex arcs
Simplest reflex actions
Sensory neurones send impulse from receptors to spinal cord -> motor neurone runs from spinal cord to muscle
=> involves only one synapse between two neurones
Very hard to inhibit
Polysynaptic reflex arcs
More complex reflexes (E.g. withdrawal reflex)
Involve interneurones to form a link between sensory neurone and motor neurone
-> more than one synapse
Sensory neurone detects noxious stimuli -> sends noxious message to spinal cord -> message communicated to interneurone -> excites motor neurone -> stimulates flexor muscle -> contraction
Can reflexes be overridden?
Yes
Noxious stimuli often evoke reflex action
-> however, if stimulus isn‘t too painful we can use voluntary control of movement to counter-act reflex
How do we inhibit reflexes?
Cortex sends signals down descending tracts that synapse with inhibitory interneurones
-> prevent motor neurone from communicating signal to muscle
What is the brainstem comprised of?
Mesencephalon (Midbrain)
Myelencephalon:
- Pons
- Medulla oblongata
Why is the brainstem vitally important for humans?
Many ascending and descending axon tracts that link spinal cord and brain pass through it
With what is the brainstem caudally continous?
With the spinal cord
With what is the brainstem rostrally continous
Diencephalon
Why is the brainstem important for the communication of sensory and motor Informationen the head?
It contains cranial nerves and cranial nerve nuclei
What are cranial nerve nuclei?
Cell bodies from which motor cranial nerves project their axons
-> innervate muscles in head and neck
Also consist of cell bodies that receive sensory information from head and neck
=> cranial nerve nuclei are either sensory or motor, not both
What is the Medulla?
An „enlarged extension“ of the spinal cord in the cranium
Contains nuclei responsible for vital reflexes (e.g. breathing, vomiting, coughing and sneezing)
What is the pons?
Contains pontocerebellar fibres (transverse system of axon fibres)
-> connect cerebral cortex and cerebellum
=> allow coordination of body movement
What is the midbrain comprised of?
Tectum
Tegmentum
-> separated by cerebral aqueduct
What is the purpose of the cerebral aqueduct?
Allows circulation of CSF
What are the swellings of the tectum called?
Superior colliculus
Inferior colliculus
What does the superior colliculus do?
Plays a key role in the visual system
What does the inferior colliculus do?
Responsible for the auditory system
What does the tegmentum contain?
Reticular formation
Periaqueductal grey matter
Red nucleus
Substantia nigra
What is the reticular formation?
Complex network of nuclei running through the core of the brainstem
Plays a role in:
- aspects of motor activity (e.g. breathing movements, cardiovascular function, muscle tone, posture and perception of pain)
- sleep
- arousal
- consciousness
- attention
What is the periaqueductal grey matter?
Surrounds cerebral aqueduct
Involved in primitive behaviours (e.g. agression and mating)
Plays role in how opiates produce analgesic (pain-relieving) effects
Opiate
Synthetic opioid
What is the red nucleus?
Origin of rubrospinal tract
-> one of the major descending pathways that takes motor information from cortex to spinal cord
What does the substantia nigra connect with?
Basal ganglia and putamen
What is the substantia nigra involved in and which neurotransmitter does it use?
Voluntary control of movement
Dopamine
How is the substantia nigra connected to Parkinson‘s disease?
Degeneration of neuronal connections between substantia nigra and basal ganglia
-> cause of Parkinson‘s disease
What is Parkinson‘s disease?
Movement disorder characterised by tremors, rigidity of limbs, poor balance and difficulty in initiating movements
≠limb apraxia
In how far are limb apraxia and Parkinson‘s different?
Limb apraxia is typically caused by damage to left hemisphere (areas associated with motor skills)
Limb apraxia primarily affects voluntary motor control
Parkinsons is caused by degeneration of dopamine-producing neurones in substantia nigra
Parkinson‘s primarily affects involuntary motor control (tremors at rest)
How many pairs of cranial nerves are there?
12
What is the difference between cranial nerves III to XII and cranial nerves I and II?
III to XII attach at different locations of the brainstem
I and II attach to the prosencephalon
What is the difference between cranial nerves and cranial nerve nuclei regarding their nature?
Cranial nerve nuclei cant be sensory and motor at the same time
Cranial nerves can be mixed
Trigeminal sensory nucleus
Receives sensory information from head (e.g. pain, temperature & touch)
Vestibular nuclei
Receive information regarding motion and position of head from vestibular organ in ear
Cochlear nuclei
Receive auditory information from inner ear
Nucleus solitarius
Receives taste information
What is important to know about the positioning of cranial nerve nuclei?
They are bilateral/ symmetrical in the brainstem
What can cranial motor nuclei be divided into?
Column 1) The somatic efferent column
Column 2) The branchiomotor column
Column 3) The parasympathetic colum
What does the somatic efferent column consist of?
The oculomotor nucleus, trochlear nucleus and abducens nucleus: control eye movement
The hypoglossal nucleus: controls movement in tongue
What does the branchiomotor column consist of?
Trigeminal motor nucleus:: innervates muscles in jaw and mouth
The facial motor nucleus: innervates facial muscles
The nucleus ambiguus: innervates muscles in pharynx and larynx
What does the parasympathetic column consist of?
Edinger-Westphal nucleus: controls pupil size
Superior and inferior salivatory nuclei: innervate lacrimal and salivary glands
Dorsal motor nucleus of the vagus: innervates internal organs
Generally speaking, what does each column of cranial motor nuclei do?
Somatic efferent column: control eye movement
Brachiomotor column: produce movement in face, pharynx (throat) and larynx (voice box)
Parasympathetic column: exert parasympathetic control over certain muscles, glands and organs
What is cranial nerve I?
Sensory nerve that communicates olfactory information
How does olfactory information reach our conscious perception? (Pathway)
Olfactory receptors in superior part of nasal cavity detect odorant particles
-> communicate information along olfactory nerve to olfactory bulb
-> shares information with different brain areas
-> conscious perception of smell
What is cranial nerve II?
Optical nerve
Each eye has one optic nerve
Information primarily sent to lateral geniculate nucleus in thalamus before being sent to primary visual cortex
What is cranial nerve III?
Oculomotor nerve
-> efferent nerve containing motor and parasympathetic fibres
What do the motor fibres of the oculomotor nerve do?
Control majority of the eye muscles
(Originate in oculomotor nucleus in mesencepthalon)
What do the parasympathetic fibres of the oculomotor nerve do?
Control iris muscles that produce pupillary light reflex
Control ciliary muscles that regulate thickness of lens for focusing
Parasympathetic neurones originate in Edinger-Westphal nucleus in mesencephalon
What is cranial nerve IV?
Trochlear nerve
-> motor nerve that controls superior oblique muscle
=> allows depressive (downward), abduct (outward) and intort (inward) eye movements
Originates in trochlear nucleus
What is cranial nerve VI?
Abducens nerve
-> motor nerve innervating lateral rectus eye muscle
=> allows abduct eye movements
Originates in abducens nucleus
What is cranial nerve V?
Trigeminal nerve
-> contains sensory and motor fibres
What nerves do sensory fibres in the trigeminal nerve consist of and what is their task?
Ophthalamic, maxillary and mandibular nerves
Carry somatosensory information from skin of face and scalp, cornea (eye), nasal cavity and mouth (including teeth and sinuses)
Attach to trigeminal sensory nucleus
What do motor fibres of the trigeminal nerve consist of and what is their task?
Mandibular nerve
Controls mastication muscles (open and close jaw)
Controls soft palate (muscles at back of mouth important for swallowing)
Controls digastric muscle (below jaw)
Originates from trigeminal motor nucleus
What else does the mandibular nerve innervate
Tensor tympani muscles in middle ear
-> dampen loud sounds
What is cranial nerve VII?
Facial nerve
-> contains sensory, motor and parasympathetic fibres
What are the sensory fibres in the facial nerve responsible for?
Receive taste information from anterior 2/3 of tongue and palate
Communicate somatosensory information from external ear
Attach to nucleus solitarious
What are motor fibres of the facial nerve responsible for?
Control of facial muscles
Originate from facial motor nucleus
What are parasympathetic fibres of the facial nerve responsible for?
Stimulate salivary and lacrimal glands
Originate from superior salivatory nucleus
What is cranial nerve VIII?
Vestibulocochlear/ statoacoustic nerve
-> sensory nerve that sends impulses from inner ear
Two components:
- vestibular nerve
- cochlear nerve
What is the vestibular nerve responsible for?
Information related to position and movement of head (comes from vestibular organ in inner ear)
Attach to vestibular nuclei
Send information to cerebellum to control equilibrium
What is the cochlear nerve responsible for?
Carries auditory information from cochlea (in inner ear)
Attaches to cochlear nuclei
What is cranial nerve IX?
Glossopharyngeal nerve
Contains sensory, motor and parasympathetic fibres
What do sensory fibres of the glossopharyngeal nerve do?
Communicate taste and somatosensory information from posterior third of tongue and pharynx
Communicate somatosensory information from middle ear
Connect to nucleus solitarius
-> important role in swallowing and gag reflexes
What do the motor fibres of the glossopharyngeal nerve do?
Innervate stylopharyngeus: muscle involved in swallowing
Originate in nucleus ambiguus
What do the parasympathetic fibres of the glossopharyngeal nerve do?
Innervate parotid salivary gland
Originate in inferior salivatory nucleus
What is cranial nerve X?
Vagus nerve
Contains sensory, motor and parasympathetic nerves
What are the sensory fibres of the vagus nerve responsible for?
Communicate somatosensory information from:
- pharynx
- larynx
- oesophagus (connects mouth and stomach)
- tympanic membrane (ear drum)
- auditory canal
- external ear
- organs in abdomen
Terminate in trigeminal nucleus/ nucleus solitarius (organs in abdomen)
What are the motor fibres of the vagus nerve responsible for?
Innervate soft palate, pharynx, larynx and upper part of oesophagus
-> important for swallowing and speech
Originate from nucleus ambiguus
What are the parasympathetic fibres of the vagus nerve responsible for?
Parasympathetic control on cardiovascular, respiratory and gastrointestinal systems
Originate from dorsal motor nucleus of the vagus
What is cranial nerve XI?
Accessory nerve
-> motor nerve originating from nucleus ambiguus
One branch innervates soft palate, pharynx and larynx
Other branch innervates trapezius and sternocleidomastoid muscles
-> allow movement in neck
What is cranial nerve XII?
Hypoglossal nerve
-> motor nerve originating from hypoglossal nucleus
Innervates tongue
-> allows ot to move and change shape
=> important for chewing movements, sucking, swallowing and speech
