Neurology Quick Facts Week 1 Flashcards
1
Q
The telencephalon encompasses the
A
cerebral hemispheres
2
Q
The diencephalon encompasses the
A
thalamus and hypothalamus
3
Q
The mesencephalon encompasses the
A
midbrain
4
Q
The metencephalon encompasses the
A
pons and cerebellum
5
Q
The rhombencephalon encompasses the
A
medulla
6
Q
The hindbrain includes the
A
reticular formation, pons, cerebellum, and medulla
7
Q
The midbrain includes the
A
superior and inferior colliculus
8
Q
Gray matter
A
High neuron density
Lines brain
Middle of spinal cord
9
Q
White matter
A
High axon density
Lines spinal cord
Middle of brain
10
Q
Basal ganglia definition and function and main players
A
A group of structures linked to the thalamus that smooth out motor movements of limbs and axial musculature during body movement. The main components are the caudate nucleus (which contains the amygdala at its tip) and putamen (together called dorsal striatum), nucleus accumbent and olfactory tubercle (together called ventral striatum), globus pallidus (which has distinct lateral and medial nuclei called GP external and GP internal nuclei), ventral pallidum, substantia nigra, and sub thalamic nucleus.
11
Q
Amygdala
A
Small ball at the tip of the caudate nucleus, within the dorsal striatum. Important center for processing memory, decision making, and emotional reactions such as fear and rage.
12
Q
Functional definition of Parkinson’s Disease
A
An interruption of the input from the substantial nigra to the caudate putamen, which reduces movement and causes Parkinsonism. The substantia nigra is the source of the striatal input of the neurotransmitter dopamine, which plays an important role in basal ganglia function.
13
Q
Thalamus
A
Important regulatory center for autonomic nervous system, consciousness, and sleep.
14
Q
Contents of brainstem
A
Midbrain, pons, and medulla. The medulla connects the brain to the spinal cord.
15
Q
Where does the adult spinal cord end?
A
The T12-L1 level
16
Q
What is the corticospinal, or pyramidal pathway? Describe the main steps of the pathway.
A
This is a motor pathway to the periphery.
It originates in the Betz cells (neurons in the motor cortex of the forebrain). These neurons send axons through the posterior limb of the internal capsule, though the anterior part of the midbrain, and through the pons, where the fibers are broken up into several bundles. The CST then descends as the “pyramids” in the anterior part of the medulla. At the junction of the medulla and spinal cord, 85-90% of the fibers cross decussate in an area called the “decussation of pyramids” to then continue as the lateral corticospinal tract, which terminates on lower motor neurons in the ventral horn of the spinal cord. The remaining fibers that did not cross continue as the Anterior, or Direct, Corticospinal Tract. The fibers of this tract decussate once they’ve reached their target - at the level of the lower motor neuron with which they synapse.
17
Q
What is the spinothalamic tract? Describe the main steps of the pathway.
A
The spinothalamic tract is a sensory pathway that serves the sensations of PAIN and TEMPERATURE from the periphery. The cell bodies for this tract are located in the dorsal root ganglion; they are pseudo-unipolar cells that send one axon to the periphery to sense pain and temperature, and one central extension of the same axon to the spinal cord.
Axons enter the spinal cord from the spinal ganglion, travel up or down through the Lissauer tract, then synapse with a secondary neuron in the dorsal horn of the spinal cord gray matter. The axons of this secondary neuron decussate and ascend as the spinothalamic tract in the spinal cord. The tract reaches the caudal medulla, ascends to the rostral medulla in between the inferior olivary nucleus and the nucleus of the spinal tract of the trigeminal nerve, and ascends farther to the pons and midbrain, where it lies lateral to the medial lemniscus. Finally the tract terminates in the VPL (ventral posterior lateral nucleus) of the thalamus, with a synapse on a tertiary neuron. That neuron sends axons to neurons in the somatosensory cortex, or postcentral gyrus, of the forebrain to complete the pathway.
18
Q
What is the posterior (dorsal) column pathway, and what are its steps?
A
The posterior column pathway informs the brain of the position of body parts in space in a position sense. The cell bodies for this pathway lie in the dorsal root ganglia; they are pseudo-unipolar cells that send one axon to the periphery to sense VIBRATION AND POSITION CHANGES, and one central extension of the same axon to the spinal cord. Axons enter the spinal cord. If they enter at the cervical or thoracic level, they ascend rostrally and ipsilaterally via the fasciculus cuneatus. If they enter at the lumbar or sacral level, they ascend rostrally and ipsilaterally via the fasciculus gracilis. Whichever the tract, their destination is the medulla of the brainstem, where they synapse to a second order neuron in either the nucleus gracilis (if nerves enter at lumbar or sacral level of spinal cord - leg afferents) or the nucleus cuneatus (if nerves enter at the cervical or thoracic level of the spinal cord - arm afferents). The secondary neuron sends its axon to decussate and form the medial lemniscus. The fibers travel as the medial lemniscus adjacent to the midline in the rostral medulla, continue through the pons, and finally laterally and vertically through the rostral pons and midbrain. The medial lemniscus terminates in the ventral posterior lateral nucleus, or VPL, of the thalamus, where it synapses on a third order neuron. This tertiary neuron sends its axons through the internal capsule to synapse with cortical neurons in the somatosensory cortex, or postcentral gyrus.
19
Q
Does the ectoderm, mesoderm, or endoderm form the nervous system?
A
The ectoderm forms the skin and nervous system.
20
Q
At how many weeks gestation does a 3 vesicle brain form? What are the vesicles?
A
Week 4
Prosencephalon, Mesencephalon, and Rhombencephalon
21
Q
At how many weeks gestation does a 5 vesicle brain form? What are the vesicles?
A
Week 5
Telencephalon, Diencephalon, Mesencephalon, Metencephalon, Myelencephalon
22
Q
The prosencephalon of the 3-vesicle brain further develops into?
A
The telencephalon and diencephalon.
The prosencephalon is also known as the forebrain.
23
Q
The mesencephalon of the 3-vesicle brain further develops into?
A
The midbrain. The mesencephalon is also known as… the midbrain.
24
Q
The rhombencephalon of the 3-vesicle brain further develops into?
A
The metencephalon and the myelencephalon. The rhombencephalon is also known as the hindbrain.
25
At how many days gestation does the anterior neural pore close?
25 days
26
At how many days gestation does the posterior neural pore close?
27 days
27
Into what type of cells do ventricular zone neuroepithelial cells differentiate?
Neuroblasts and glioblasts. These cells are generated in the ventricular zone of the neural tube and migrate out to their final destination.
28
Neuroblasts form which cells of the central nervous system?
They form all of them.
29
The glioblasts form which cells of the nervous system?
They form radial glial cells, astrocytes, oligodendrocytes, ependymocytes, tanycytes, and choroid plexus cells.
30
From which cells do microglia arise? What is the function of microglia?
They arise from monocytes in circulation that invade the CNS during the third week, along with the formation of the cerebral blood vessels.
31
What is the function of radial glial cells?
They serve as guide wires for the migration of neurons, which attach to said "wires", or cells, and travel to their final destination.
32
What separates the alar plate from the basal plate within the embryo neural tube?
The sulcus limitans separates the alar plate from the basal plate. Eventually, the sulcus laminates will separate the sensory brain stem nuclei from the motor brain stem nuclei in the adult brain.
33
Alar plate neurogenesis creates what class of neurons?
Sensory neurons of what will become the dorsal sensory horn
| Thus, the dorsal root ganglia neurons are also derived from the alar plate.
34
Basal plate neurogenesis creates what class of neurons?
Motor neurons of what will become the ventral horn.
35
Dorsal root ganglia and various autonomic and enteric ganglia are produced from what embryonic structure/cells?
Neural crest cells
36
What is the consequence of a filum terminale connection that is too tight? (The filum terminale connects the conus modullaris to the coccygeal ligament.)
Tethered spinal cord syndrome, in which children present with back pain, leg pain, leg weakness, scoliosis, and loss of bowel and bladder control.
37
Common birth defects if anterior neural pore fails to close
Anencephaly and encephalocele
38
Common birth defects if posterior neural pore fails to close
spina bifida, meningocele, myelomeningocele
39
What's a good thing to test for when you suspect a neural tube defect?
alpha-fetal protein
40
Anencephaly
Absence of forebrain due to failure of the cephalic (anterior) portion of the neural pore to close. No higher cognition because no forebrain, but can breathe because the medulla is ok.
41
By what week of gestation has the neural plate formed?
Week 3
42
What tissues fuse to form the neural tube?
The neural folds
43
Encephalocele
Occurs when the anterior portion of the neural pore fails to close. The brain and meninges protrude through openings in the skull, and there are usually other craniofacial abnormalities.
44
Spina bifida occulta
Failure of the bony spinal canal to close because the mesodermal cells did not form bony dorsal vertebrae to surround the spinal cord. The meninges and spinal cord are NOT involved. Look for a tuft of hair over the lumbar-sacral area or a sinus tract at clinical presentation.
45
Spina bifida aperta with meningocele
Failure of bony spinal canal to close; accompanied by meningocele, in which the meninges extend in an outpouching. Meninges only; spinal cord stays in canal.
46
Spina bifida with myelomeningocele
Failure of bony spinal canal to close; accompanied by myelomeningocele, in which meninges AND spinal cord/filum terminale extend into an outpouching.
47
Chiari Type I
The cerebellar tonsils extend into the foramen magnum WITHOUT involving the brainstem. Usually presents in adulthood, or by incidental finding in exam. Patients present with headache because outflow of the cerebral spinal fluid into the spinal canal becomes obstructed, and the intracranial pressure increases to cause headache.
48
Chiari Type II
This the most common pediatric form of Chiari. There is significant herniation of cerebellar tonsils and vermis (the vermis connects the two halves of the cerebellum) through the foramen magnum; in other words, the brain stem tissue and the cerebellum are herniating through the foramen magnum. Usually accompanied by a lumbosacral meningocele with paralysis below this defect.
49
What are the two potential spaces associated with the meninges?
The epidural space (between the dura periosteum and the skull bones) and the subdural space (between the meningeal dura and the arachnoid mater) are potential spaces because they normally don't exist until head trauma causes hemorrhage into them.
50
Where do arteries and veins lie within the meninges? What occurs with rupture of the vessels?
The subarachnoid space
Rupture of the vessels would cause hemorrhage into the subarachnoid space
51
Which meningeal layer forms the epineurium?
The dura mater (now only a single layer)
52
Which meningeal layer forms the perineurium?
The arachnoid mater
53
Which two major pairs of arteries supply the brain?
The right and left internal carotid arteries
The right and left vertebral arteries
54
What do the external carotid arteries supply?
The face, scalp, and meninges overlying the brain. The middle meningeal artery branches off the external carotid artery. Skull fracture can rupture the vessel and cause an epidural hemorrhage, leading to death in just a few short hours.
55
What path do the internal carotid arteries take into the cranium? What happens once they're there?
After ascending through the carotid canal, they enter the cranial vault along the cavernous sinus, make a hairpin turn backwards, and continue on as the middle cerebral artery and the anterior cerebral artery. The first branch of the internal carotid artery is the ophthalmic artery.
56
Describe the path of the vertebral arteries
The vertebral arteries originate from the subclavian arteries and enter the vertebral foramen at the level of C6. They ascend through spinal foramen to enter the calvaria through the foramen magnum, joining at the junction of the pons and medulla to form the basilar artery.
57
Result of rupture of middle meningeal artery?
Epidural hemorrhage and death in hours.
58
Who is in the Circle of Willis club? What is the point even?
The posterior cerebral arteries connect to the internal carotid arteries via the posterior communicating arteries. The anterior segment of the anterior cerebral artery (A1), and the anterior communicating artery complete the Circle of Willis. The Circle of Willis provides potential for collateral blood flow if one or more of the four major arteries supplying the brain becomes obstructed.
59
What are the two principal cell types in the nervous system?
Neurons and glia
60
Describe the three main structural components of a neuron, and the function each structure has
Neurons are composed of a soma, one or more dendrites with their dendritic spines, and a single axon.
The soma houses the nucleus and makes proteins.
Dendrites receive synaptic input. Dendritic spines protrude from the dendrite, receiving inputs and transmitting electrical signals to the dendrite.
The axon generates electrical signals, so it's the electrical output for the cell. It originates from the soma, first forming an axon hillock, which is free of organelles.
61
Describe where Nissl bodies are, what they contain, and what they do
Nissl substance contains mostly rER and ribosomes. It extends from the soma into the base of each dendrite, but does NOT extend into the axon.
62
Describe a pyramidal neuron.
A pyramidal neuron has a pear-shaped soma and both apical and basal dendrites.
63
Explain from whence an axon begins, and its general path and anatomy after its genesis
The axon originates from the soma, first forming the axon hillock, which is free of organelles.
A myelinated axon: the portion from the axon hillock to the beginning of myelination is termed the axonal initial segment, and it is where action potentials begin. The axon then splits into major branches called collaterals, which may branch further. These extensions contact other neurons or effector organs.
64
What is the purpose of myelin?
Myelination is an electrical insulator that facilitates faster nerve conduction of action potentials along the axon.
65
Neurons whose axons contact muscles or glands are called?
Motoneurons.
66
Classify the structure of a dorsal root ganglion cell
Pseudounipolar neuron
67
What are interneurons? By what other names are they known?
Interneurons do not send their axons out of the local brain area. They are also known as local circuit neurons and are classified as Golgi Type 2 cells.
68
What do principal cells do?
They are projection neurons.
They integrate information and send axons to other brain areas. They are classified as Golgi Type I cells.
69
What are the two types of synapses, and how do they function?
1) An electrical synapse forms a direct connection with another cell through gap junctions. They are bi-directional and allow passage of a direct, passive flow of electrical current.
2) A chemical synapse entails an electrical signal in the presynaptic neuron being transduced into the release of a chemical transmitter that then traverses the synaptic cleft to bind receptors on the post-synaptic neuron. These connections are uni-directional (Pre to Post always).
70
A synapse between a neuron and a muscle is called a?
Neuromuscular junction
71
In the brain, where are most excitatory synapses formed?
On dendritic spines; called an axospinous synapse, a subset of axodendritic synapses, which are axons that contact dendrites.
72
On an incoming nerve impulse, entry of ________ causes synaptic vesicles to release their contents into the synaptic cleft
Ca2+
73
What are three functions of synapses, and what do they do?
Excitatory synapses increase the likelihood that the postsynaptic neuron will fire an AP. They are Gray's Type 1 synapses and have pronounced postsynaptic density.
Inhibitory synapses decrease this likelihood.
Modulatory synapses influence how excitatory and inhibitory signals are integrated.
74
Synapses that are excitatory are classified as? They have _______ postsynaptic density. They are usually found on ________.
Gray's Type I
pronounced
dendrites
75
Synapses that inhibitory are classified as? They have _______ postsynaptic density. They are usually found on _______?
Gray's Type 2
comparable pre-synaptic and...
the soma
76
Describe the anatomy of a gap junction
The gap junction is composed of one connexon from each cell participating in the gap junction. A connexon is made of 6 connexins. When the connexon from each cell becomes opposed, a low-resistance pore called a gap junction is formed.
77
Role of kinesin
Moves cargo along microtubules from the soma to the cargo's destination. This is also called "anterograde movement"
78
Role of dynein
Move cargo along microtubules toward the soma. This is also called "retrograde movement'
79
Non-excitable cells of the nervous system are also known as ________
Supporting cells
80
Neuroglia - role and types of neuroglia
A group of supporting cells that make up 50% of brain volume.
The types of neuroglia are Schwann cells, oligodendrocytes, and astrocytes (of which there are also 2 types: fibrous and protoplasmic astrocytes)
81
Schwann cells
A type of neuroglial cell that provides myelination in the peripheral nervous system. They improve electrical insulation to increase conduction velocity for action potentials. Individual Schwann cells wrap around one axon, and where they touch, a Node of Ranvier (internode) is formed. It is an unmyelinated area where action potential regenerate.
Schwann cell myelin is in contact with Schwann cell soma.
82
Oligodendrocytes
A type of neuroglial cell that provides myelination in the CNS. Each oligodendrocyte has several processes, each of which provides myelination for one axon. This is a difference between them and Schwann cells: oligodendrocytes myelinate several axons/have many internodes, whereas Schwann cells myelinate only one axon/form one internode. Neighboring internodes can therefore originate from different oligodendrocytes.
Oligodendrocyte myelin is not necessarily in contact with its soma due to its long processes.
83
Astrocytes
A type of neuroglial cell that serves as part of the blood brain barrier in the CNS. They facilitate angiogenesis and synaptogenesis.
They move metabolites to and from neurons in a process called metabolic exchange.
They maintain constant ionic concentrations
They have radiating processes that contact neurons; these are called perineurial feet.
They have radiating process that contact endothelial cells; these are called perivascular feet.
They have radiating processes that contact myelin.
84
How are the lamellae of lipid and Schmidt-Lanterman clefts formed?
As the Schwann cell wraps tightly around the axon, the cytoplasm of the cell is squeezed out, leaving behind layers of lipid called lamellae. Small folds of cytosol remain to support the myelin; they are called Schmidt-Lanterman clefts.
85
The _______ surrounds a fascicle. They fascicle contains many axons, each surrounded by a thin layer of connective tissue called the _______. Each axon is ______ if in the periphery.
perineurium
endoneurium
myelinated
86
What do you know about fibrous astrocytes?
They are found in the white matter of the CNS. They have vascular feet that physically connect them to the outside of capillary walls
87
What two types of radial glia persist into adulthood?
Bergmann glia and Mueller cells
88
What do you know about protoplasmic astrocytes?
They are located in grey matter and the most common type.
89
What do you know about radial glia?
They are a type of microglia present during development. They facilitate neuron migration.
90
Satellite Cells: what, where, etc.
Satellite cells originate from the neural crest and are modified Schwann or oligodendrocyte cells. They function as astrocytes in peripheral ganglia, surrounding the entire soma of ganglion cells.
91
Ependymal cells: what, where, etc.
These line the ventricles of the brain and the central canal of the spinal cord. They are usually ciliated and cuboidal or columnar in shape. They make CSF, and because they lack tight junctions, can allow free exchange between CSF and nervous tissue.
92
In an anterior view of the skull, through which opening does CN II pass?
CN II passes through the optic canal.
93
In an anterior view of the skull, what nerves pass through the superior orbital fissure?
CN III, IV, VI, and the V1 branch of CN V
94
What does the ophthalmic (V1) branch of the trigeminal nerve do?
It transmits sensory information from the ipsilateral forehead and scalp to the brainstem
95
What passes through the cribriform plate? Result of trauma?
Fibers from the overlying olfactory bulb on their way to reach the nasal epithelium. Trauma shears the fibers to produce anosmia.
96
What travels in the optic canal?
The optic nerve
97
What passes through the foramen rotundum?
The V2 (maxillary) branch of the trigeminal nerve
98
What passes through the foramen ovale?
The V3 (mandibular) branch of the trigeminal nerve
99
What passes through the foramen spinosum?
The middle meningeal artery ENTERS the skull through the foramen spinosum.
100
Describe the path of the facial nerve (CN VII) in the skull
CN VII enters the internal auditory canal/meatus (AKA: acoustic meatus) and exits the skull via the stylomastoid foramen
101
Describe the path of CN VIII
CN VIII enters the internal auditory canal and exits the skull through the external auditory meatus.
102
What exits through the jugular foramen?
CN IX, X, and XI EXIT the skull through the jugular foramen
103
How does CN XII exit the skull?
The hypoglossal canal
104
Describe the path of CN XI
CN XI spinal branches pass rostrally through the foramen magnum to enter the skull, join the cranial branches, and exit through the jugular foramen.
105
How does the internal carotid artery enter the skull?
It gain access through the carotid foramen, then passes through a bony canal, then finally enters the skull through the carotid canal.
106
What are two areas within the skull that, if trauma occurs, can injure the brain?
The lesser wing of the sphenoid bone and the petrous ridge of the temporal bone
107
How are the superior sagittal sinus and lateral sinuses created?
The two layers of the dura mater, the meningeal layer (closest to the brain) and the periosteal layer (closest to the skull bones), separate at the midline and at the lateral aspects of the brain to create the large venous sinuses
108
How is the falx cerebri created?
The meningeal layers of both side of the brain, still separated from the periosteal layers, come together to create the thick membrane called the falx cerebri, which separates the left and right cerebral hemispheres.
109
How is the tentorium cerebella created?
The meningeal layers, still separated from the periosteal layers, come together to create the tentorium, which separates the cerebral hemispheres from the cerebellar hemispheres in the posterior fossa.
110
What is contained in the subarachnoid space?
The subarachnoid space contains most of the cerebrospinal fluid that bathes the brain. It also contains large blood vessels - arteries and veins.
111
Where does the middle meningeal artery come from?
The middle meningeal artery branches off of the external carotid artery.
112
What structures drain blood from the brain? What occurs when these drainage sites are blocked?
The cavernous sinus, the straight sinus, the superior sagittal sinus, the inferior sagittal sinus, the transverse sinus, and the great cerebral vein of Galen.
Blockage can cause seizures, tissue injury, and blockage of CSF circulation.
113
What is the method of communication between the lateral ventricles with the midline third ventricle?
Left interventricular foramen of Monro
114
What is the method of communication between the third and fourth ventricles?
The cerebral aqueduct of Sylvius, or the Sylvian aqueduct
115
Where is CSF created?
CSF is created in the choroid plexus by epithelial cells that line the lateral, third, and fourth ventricles.
116
What is the path of CSF through the brain?
CSF drains from the lateral ventricles, down the foramen of Monro, and into the third ventricle. It then flows down the aqueduct of Sylvius into the fourth ventricle. It leaves the fourth ventricle by the foramina of Magendie and Luschka to enter the subarachnoid space. In the subarachnoid space, some CSF circulates around the spinal cord, where 10% of it is reabsorbed through the nerve roots. The rest of the CSF travels upward, through an opening in the tentorium cerebelli, and over and around the brain. It is reabsorbed into the venous sinuses via the arachnoid granulations that are outpouchings of the arachnoid (called arachnoid villi) that protrude into large venous sinuses .
117
What is the result of a blocked CSF outflow pathway?
Tumors or blood clots can obstruct CSF flow. This causes increased intracranial pressure and hydrocephalus.
118
What are arachnoid villi?
These guys function as one-way valves for CSF to flow out of, but not back into, the ventricular system. Obstruction of one-way valves can cause CSF to back up, leading to hydrocephalus.
119
Non-obstructive hydrocephalus or communicating hydrocephalus
Occurs when only arachnoid villi become obstructed. CSF can still flow throughout ventricles; it just cannot leave the ventricles.
120
Obstructive hydrocephalus
Caused by physical blockage of the ventricular system so that CSF cannot flow throughout the ventricles, leading to an increase in intracranial pressure and hydrocephalus.
121
Explain the anatomy of endothelial cells lining the brain capillaries.
Capillaries in the brain do not have fenestrations. These cells have tight junctions that cause adjacent cells to be tightly approximated to each other. This forces substances from capillaries to pass through endothelial cells, instead of in between them. Astrocytes provide an extra level of protection in that they extend their end feet onto the capillary, lining it.
122
How is the choroid plexus created?
It is created by outpouchings of capillaries and the pia mater into the ventricular space. The capillaries are sandwiched between the arachnoid membrane and pia mater.
123
What are ventricular ependymal cells?
These are cells that line the ventricular wall only. They are NOT called as such when they line the choroid outpouchings (see choroid epithelial card). Ventricular ependymal cells possess the normal fenestrations seen in capillaries elsewhere.
124
What are choroid epithelial cells?
These are epithelial cells that line choroid outpouchings. They contain a tight junction to limit the potentially toxic substances circulating in the capillaries from entering the CSF space.
125
What are circumventricular organs
Areas of the brain where there is no blood brain barrier. These areas do not have a BBB because they monitor and regulate blood chemistry, so they need direct access to blood born chemicals.
126
What are the Organum vasculosum and the neurohypophysis?
These are circumventricular organs that lack a blood brain barrier. The organum vasculosum regulates electrolyte balance, and the neurohypophysis regulates hormones
127
What is the glymphatic system?
This is a functional waste clearance pathway for the CNS. It has a para-arterial inflow path for CSF to enter the brain. The CSF, which contains solutes, enters the brain and exchanges these solutes with the interstitial fluid via convective bulk flow that is facilitated by astrocytic aquaporin 4 water channels.
128
How are adrenergic receptors sub-classified?
How are cholinergic receptors sub-classified?
There are alpha and beta adrenergic receptors.
There are nicotinic and muscarinic receptors
129
What are the divisions of the autonomic nervous system?
Sympathetic
Parasympathetic
Enteric
130
What neurotransmitter is used at preganglionic sympathetic and parasympathetic synapses?
Ach
131
Explain innervation of the adrenal gland
The adrenal gland receives a sympathetic, direct, preganglionic innervation with Ach.
132
Post-ganglionic parasympathetic neurons use what neurotransmitter?
Ach
133
Post-ganglionic sympathetic neurons use what neurotransmitter?
Norepinephrine
134
Post-ganglionic sympathetic innervation of sweat glands and erector pili use what neurotransmitter?
Ach
135
Sympathetic effect on the eye
Contracts the pupil dilator, or radial, muscle to dilate the pupil and relaxes the ciliary muscle to flatten the lens and allow for far vision. Contracts the tarsal muscle to keep the eyelid open.
136
Parasympathetic effect on the eye
Contracts the pupil constrictor muscle, or circular muscle, to constrict the pupil and contracts the ciliary muscle of the lens to allow for near vision (accommodation)
137
What doe the ciliary muscle do?
It controls accommodation for viewing objects at varying distances. It changes the shape of the lens within the eye, but does NOT change the size of the pupil.
138
Sympathetic effect on the lacrimal, salivary, parotid, and sweat glands
Thickens salivary secretions and stimulates sweat glands. No effect on lacrimal glands
139
Parasympathetic effect on the lacrimal, salivary, parotid, and sweat glands
Increases secretions from the lacrimal gland and causes watery secretions from the salivary glands
140
Sympathetic effect on the cardiac muscle, coronary arteries, and the SA and AV nodes
Increases contraction force of the muscle
Alpha receptors constrict coronary arteries, and Beta receptors dilate arteries
SA and AV nodes fire at an increased rate with increased conduction
141
Parasympathetic effect on the cardiac muscle, coronary arteries, and the SA and AV nodes
Decrease contraction force
Dilate coronary arteries
SA and AV nodes fire an a decreased rate with decreased conduction.
142
Sympathetic effect on arterioles of the skin and skeletal muscles
Alpha receptors in the skin constrict blood vessels
Beta receptors in the skeletal muscle dilate blood vessels.
Blood vessels in the lungs, abdominal viscera, and renal areas are also dilated.
143
Parasympathetic effect on arterioles of the skin, skeletal muscles, pulmonary system, abdominal viscera, and renal system
Dilation of blood vessels
144
Sympathetic effect on the lung
Relaxes because dilates bronchi
145
Parasympathetic effect on the lung
Contracts because constricts bronchi
146
Sympathetic effect on GI
Inhibits peristalsis of the wall muscle
Contracts sphincter muscles
Decreases secetions
147
Parasympathetic effect on GI
Stimulates peristalsis
Relaxes sphincter muscles
Increases secretions.
148
Sympathetic effect on the pancreas
Decreases insulin secretion and increases glucagon secretion
149
Parasympathetic effect on the pancreas
Increases insulin-glucagon secretion
150
Sympathetic effect on the liver
Stimulates glycogenolysis
151
Sympathetic effect on the adrenal gland
Stimulates epi/norepinephrine release
152
Sympathetic effect on the ureters and bladder
Relaxes the wall muscle of the bladder
Contracts the sphincter
153
Parasympathetic effect on the ureters and bladder
Contracts the wall muscle of the bladder
Relaxes the sphincter
154
Sympathetic effect on reproductive erectile tissue
Stimulates ejaculation
155
Parasympathetic effect on reproductive erectile tissue
Relaxes tissue to cause an erection
156
Describe the preganglionic spinal outflow for the sympathetic system
The secondary neuron originates in the intermediolateral zone of the spinal cord gray matter. Its axon exits the spinal cord via the ventral root and travels through a short segment of peripheral nerve to enter the white communicating ramus to gain access to the paravertebral sympathetic chain ganglia. In the ganglia, it may travel up or down to synapse, synapse at the level of entry, or exit the chain to synapse in a more peripherally located paravertebral ganglion. Whatever its path, it leaves the paravertebral sympathetic chain via the gray ramus communicans to get to the periphery.
157
The preganglionic parasympathetic fibers travel to the sigmoid colon, rectal and bladder sphincter muscles, the prostate, and other genital organs originate in which part of the spinal cord?
S2 - S4
158
Where do preganglionic parasympathetic fibers originate?
The cranial and sacral areas of the nervous system. This is why it's called the craniosacral system.
159
Where is the myenteric, or Auerbach, plexus located? What does it do?
In between the longitudinal and circular muscle layers of the intestines. It regulates gut smooth muscle and therefore gut motility.
160
Where is the Meissner plexus located?
In between the submucosa and mucosa. It regulates glandular secretions and intestinal absorption.
161
What is the final common pathway of gut motility, and what is the neurotransmitter used?
The enteric nervous system is the final common pathway. Ach is used as the effector neurotransmitter.
162
Describe the path of the sympathetic neurons that innervate the eye
A primary sympathetic neuron originates in the hypothalamus and descends through the brainstem and spinal cord to the T1 level, where it synapses with a secondary neuron in the intermediolateral gray area of the spinal cord. The axon of the secondary, preganglionic neuron send its axon out of the cord at the T1 - T2 level and into the superior cervical ganglion, where it again synapses. The tertiary, post-ganglionic neuron sends its axons within the carotid sheath to enter the skull. They travel along the short and long ciliary nerves to reach the tarsal muscles and the dilators of the iris.
163
What happens if a lesion occurs to the sympathetics traveling to the tarsal muscle and dilator muscle of the eye?
Lesion of sympathetic fibers anywhere between hypothalamus and ciliary nerve causes Horner's syndrome ON THE SAME SIDE of the lesion.
A lesion to sympathetic fibers at the level of the brainstem or spinal cord would cause loss of sweating to the entire body on the same side as the lesion because all sympathetic function below the lesion would be lost.
A lesion to the T1-T2 nerve root, or further down the line, would cause loss of sweating only to the left face, head, and neck.
164
Describe how neurons and chemo- and baroreceptors interact to regulate blood pressure.
Chemoreceptors in the carotid body send information about the carbon dioxide and oxygen content in the blood on afferent fibers of CNs IX and X. The afferents run to the solitary nucleus, where they synapse with either an interneuron that connects the solitary nucleus to the nucleus ambiguus, or one that connects the solitary nucleus to the dorsal motor nucleus of the vagus. Both the dorsal motor nucleus and the nucleus ambiguus send parasympathetic motor efferents to the heart. Lastly, the solitary nucleus also connects to midbrain sympathetic neurons to send efferent sympathetic fibers to the heart.
Baroreceptors of the heart and blood vessels relay information about blood pressure. Afferents have their cell bodies in the inferior ganglia of CNs IX and X. They send the information on to the solitary tract of the nucleus
165
What controls bladder emptying prior to the age of 3?
the pontine micturition center, which has involuntary control over the bladder.
166
What controls bladder emptying after age 3?
The medial surface of the frontal gyrus develops voluntary control over the pontine micturition center, allowing an individual to control when he wants to urinate.
The PMC stimulates sympathetic relaxation of the bladder detrusor muscle and stimulates sympathetic contraction of the internal sphincter in males to hold urine in the bladder.
To empty the bladder, the PMC stimulates the parasympathetic contraction of the detrusor muscle, inhibits sympathetic relaxation of this muscle, inhibits sympathetically mediated contraction of the internal sphincter in males, and inhibits the voluntary control of the external sphincter in both males and females.
167
Describe how pain and temperature of bladder mucosa are communicated.
Pain and temperature afferents travel with sympathetic and parasympathetic fibers to the spinal cord, decussate, and travel with the spinothalamic tract to the thalamus, and then onto the cortex.
168
How is bladder fullness sensed?
Bladder fullness is sensed by mechanoreceptors in the bladder wall and transmitted to the spinal cord with parasympathetic fibers. The fibers travel in the spinothalamic tract to reach the thalamus and eventually, the cortex.
169
How is "very full" bladder sensed?
Bladder very-fullness is sensed by mechanoreceptors in the trigone of the bladder. These fibers travel in the posterior columns to the thalamus, and eventually, the cortex. The parasympathetic system innervates the bladder detrusor muscle and causes it to contract so that bladder emptying is achieved.
170
What effects do the sympathetic and parasympathetic systems have on the bladder detrusor muscle?
The parasympathetic system innervates the bladder detrusor muscle to cause it to contract and empty.
The sympathetic system innervates the bladder detrusor muscle to cause it to relax, allowing the bladder to fill with urine. In addition, in males, the sympathetic system innervates their internal urethral sphincter to cause contraction of the sphincter muscle, closure of the urethra, and therefore, urine retention.
171
What two pathways convey somatosensory information from the periphery of the body to the brain?
The protopathic and epicritic systems
172
What information does the protopathic system carry?
The protopathic pathway carries pain, crude touch, and temperature sensation to the brain
173
What information does the epicritic pathway carry?
The epicritic pathway carries fine touch, including information about the form and texture of objects, pressure on the skin or body, position of muscles and joints, slippage, and vibration sense.
174
What tract is associated with the epicritic system?
Within the spinal cord, epicritic information travels in the posterior and the posterolateral columns, which become the medial lemniscus tract in the brainstem.
175
What tract is associated with the protopathic system?
Within the spinal cord, information travels in the anterolateral funiculi in the spinothalamic tract.
176
How do sensory receptors in skin, muscles, joints, and visceral organs communicate with the CNS?
usually via peripheral processes of pseudo unipolar sensory neurons, which have a cell body in a dorsal root ganglion. Action potentials in the DRG continue with dorsal roots to the dorsal horn of the spinal cord. Depending on the type of pathway, the processes either synapse in the dorsal horn or continue up the spinal cord to the brainstem.
177
What is a Pacinian corpuscle
It is a large, lamellar, rapidly-adapting mechanoreceptor that detects gross pressure and vibratory skin stimuli.
When pressure is first applied, an action potential is generated at that time. No other action potential is generated until the pressure is relieved. Thus, this organ signals onset and offset of the stimulus, but nothing during maintained stimulus.
178
What is a Meissner's corpuscle?
It is a rapidly adapting skin mechanoreceptor that is sensitive to light touch and vibration
179
What are Merkel's disks?
These are slowly adapting mechanoreceptors located in skin and mucosa. In fingertips, they are located under the ridges of the fingertips. In hairy skin, they are located in touch domes, or hair disks.
180
What are Ruffini organs?
These are slowly adapting mechanoreceptors found in deep layers of the glabrous skin that respond to deep pressure and skin stretch.
181
What are free nerve endings?
They do not have accessory structures associated with them to form a sense organ. They are responsive to pain and temperature
182
Define adaptation
Reduced response in the face of continued, constant stimulus.
183
Do afferents of the epicritic/lemniscal pathway decussate or remain ipsilateral on their way to the posterior column nuclei?
These fibers remain ipsilateral on their path through the dorsal column of the spinal cord and into the medulla of the brainstem
184
Where do afferents of the epicritic/lemniscal pathway that entered the spinal cord in the lumbar and sacral areas (T7 and below) synapse?
1) One of two posterior column nuclei in the medulla; in this case, gracilis nucleus
2) Ventral posterolateral nucleus (VPL) of the thalamus
3) Primary somatosensory cortex located in the postcentral gyrus.
185
Where do afferents of the epicritic /lemniscal system travel if they are trying to get to the gracilis nucleus?
They travel in the fasciculus gracilis, the most medial posterior column.
186
Do epicritic/lemniscal afferents ever decussate?
Yes, but they do so only after synapsing in one of the two posterior column nuclei in the medulla.
187
Where do afferents of the epicritic /lemniscal pathway that entered the spinal cord at T6 and above synapse?
1) One of two posterior column nuclei in the medulla; in this case, the cuneatus nucleus
2) Ventral posterolateral nucleus (VPL) of the thalamus
3) Primary somatosensory cortex located in the postcentral gyrus.
188
Where do afferents of the epicritic/lemniscal system travel if they are trying to get to the cuneatus nucleus?
They travel in the fasciculus cuneatus, the more lateral posterior column.
189
What are the two posterior column nuclei, and which kind of afferents do they interact with?
The two nuclei are the cuneatus nucleus and the gracilis nucleus. They interact with epicritic afferents. The cuneatus nucleus interacts with fibers that entered the spinal cord at T6 and above. The gracilis nucleus interacts with fibers that entered the spinal cord at T7 and below.
190
In what tract do epicritic/lemniscal afferents travel on their way from the posterior column nuclei to the thalamus?
The medial lemniscus
191
Usually pain and temperature receptors are unspecialized free nerve endings. What path do these afferents take to convey information?
They take the protopathic pathway.
192
Do afferents of the protopathic pathway decussate?
Yes, they do so immediately after entering and synapsing in the dorsal horn.
193
Where do the afferents of the protopathic pathway synapse?
1) The ipsilateral dorsal horn of the spinal cord
2) VPL of the thalamus
3) Primary somatosensory cortex in the postcentral gyrus
194
After synapsing in the ipsilateral dorsal horn, protopathic fibers travel to what? Where do the fibers travel after that?
The contralateral anterolateral funiculus
They then travel up the anterolateral spinal cord in a pathway called the spinothalamic tract to get to the brainstem and thalamus after that.
195
Where specifically do fibers in the protopathic pathway decussate?
Fibers synapse in the dorsal horn, then decussate in the anterior commissure of the spinal cord to reach the contralateral anterolateral funiculus.
196
The epicritic/lemniscal fibers that decussate in the caudal medulla are also called?
The internal arcuate fibers.
197
When epicritic/lemniscal fibers travel from the VPL to the cortex, what structure do they pass through on their way?
They travel through the posterior limb of the internal capsule.
198
Is the gracile nucleus or the cuneate nucleus more medial? Why am I asking this question?
The gracile nucleus is more medial than the cuneate nucleus. This point is made because fibers from the T7 and below add to the spinal cord first. You want them to head to the most medial position so that fibers that add in at T6 and above can simply join the party on the lateral side - where the cuneate nucleus is.
199
Which Rexed laminae are contained in the dorsal horn of the spinal cord?
Rexed laminae I - V
200
Which Rexed laminae are in the intermediate zone of the spinal cord?
Rexed laminae VI - VII
201
Which Rexed laminae are in the ventral horn of the spinal cord?
Rexed laminae VIII - IX
202
Proprioceptive afferents send collaterals to deep layers of the dorsal horn and to the ventral horn. What is an example of a collateral that goes to the ventral horn?
1a afferents from spindle and Golgi tendon organs
203
In which Rexed laminae do protopathic fibers usually synapse?
Layers I and V
204
What is the spinothalamic tract? With which fibers is it associated?
This is the pathway that runs from the contralateral anterolateral funiculus to the VPL of the thalamus.
It is associated with the protopathic pathway
205
What is Lissauer's tract?
When protopathic fibers enter the spinal cord, some travel 2-3 segments in Lissauer's Tract before synapsing in the dorsal horn.
Lissauer's Tract is also known as the posterolateral fasciculus.
206
What is the clinical importance of Lissauer's tract?
Because this tract allows protopathic neurons to travel 2-3 segments before synapsing in the dorsal horn, lesions at a given spinal cord level may result in loss of inputs 2-3 segments below the lesion.
207
What is the spinocerebellar tract?
This tract is a collection of axons that originate in the spinal cord and terminate in the cerebellum on the ipsilateral side. It conveys info about limb and joint positions to the cerebellum, usually from spindle and Golgi tendon organs.
208
What information does the dorsal spinocerebellar tract convey? Where do they go from there?
Info from spindles and Golgi tendon organs from the ipsilateral leg and body. They run in the fasciculus gracilis and synapse in Clarke's nucleus. These axons from Clarke's Nucleus have now become the dorsal spinocerebellar tract. They project into the inferior cerebellar peduncle
209
What information does the ventral spinocerebellar tract convey?
Info from Golgi tendon organs from the ipsilateral leg and body
210
What information does the cuneocerebellar tract convey?
Info from spindles and Golgi tendon organs from the ipsilateral arm
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What information does the rostral spinocerebellar tract convey?
Info from the Golgi tendon organs from the ipsilateral arm.
212
What fibers synapse in Clarke's nucleus?
Spinocerebellar tract afferents from spindle and Golgi tendon organs that have taken the dorsal spinocerebellar tract to pass via the fasiculus gracilis to Clarke's Nucleus.
213
How do dorsal spinocerebellar axons from Clarke's Nucleus project to the cerebellum?
They project to the cerebellum via the inferior cerebellar peduncles.
214
Where do afferents in the cuneocerebellar tract synapse? Where do they go from there?
They synapse in the accessory cuneate nucleus. Secondary axons project to the ipsilateral cerebellum via the inferior cerebellar peduncle.
215
Explain the path of the rostral spinocerebellar tract
The rostral spinocerebellar tract synapses at the dorsal horn of the spinal cord and ascends ipsilaterally to the cerebellum thru the inferior cerebellar peduncle
216
Explain the path of the ventral spinocerebellar tract
The ventral spinocerebellar tract synapse at the dorsal horn of the spinal cord, the decussates to ascend in the lateral funiculus to synapse with neurons in the region of the superior cerebellar peduncle. From there, a few fibers once again decussate to once again end up on the ipsilateral cerebellum.
217
What is the substantia gelatinous?
It is Lamina I and II of spinal cord gray matter. it is the initial site of integration of pain and temperature information.
218
What is the posterolateral fasciculus?
It is Lissauer's Tract, the tract in which protopathic fibers carrying pain and temperature information ascend/descend a bit before synapsing in the dorsal horn.
219
For the both epicritic and protopathic paths, what do fibers pass through on their way from the thalamus to the cortex?
The posterior limb of the internal capsule.
220
What are the three divisions of the protopathic pathway?
The spinothalamic tract, the spinoreticular tract, and the periaqueductal gray, or spinomesencephalic tract. These three pathways work together to report and solve problems. E.g.: if you step on a nail, the spinothalamic pathway reports the sharp object, the spinoreticular pathway reports the pain, and the spinomesencephalic pathway modulates the pain.
221
How are ascending axons added to the spinal cord in the protopathic pathway?
Axons are added medially, in contrast to the epicritic system
222
What are two additional synapses utilized by collateral spinothalamic tract axons of the protopathic pathway?
The intralaminar nucleus, which projects throughout the cortex to enact general arousal, and the dorsomedial nucleus of the thalamus, which projects to the prefrontal cortex.
223
What is the propriospinal tract?
This tract contains short fibers that run between spinal cord segments from the substantia gelatinosa. It is part of the protopathic pathway.
224
Protopathic pathway: Cells located specifically where in the dorsal horn send their axons to decussate and ascend the cord?
Layer V, the deepest part of the dorsal horn
225
Which fibers mediate "first pain" of the protopathic pathway?
Adelta fibers, which synapse in the substantia gelatinosa.
226
Which fibers mediate "second pain" of the protopathic pathway?
C fibers are associated with this duller, less localizable aspect of pain. They synapse in the substantia gelatinosa, especially in Layer 1. It is the Layer 1 cells that send their axons across the midline and up the cord.
227
Where do somatosensory afferents for the head have their cell bodies?
Ganglion outside of the brain known as the trigeminal ganglion
228
When trigeminal projections head to the thalamus, where specifically in the thalamus do they go?
The ventral posteromedial nucleus. The VPM receives somesthetic information from the face.
229
Where are cell bodies for the afferents for muscles of mastication located?
The mesencephalic nucleus (unlike other CN V cell bodies, which are in the trigeminal ganglion and project to the brainstem). Fibers from the mesencephalic nucleus project bilaterally to the motor nucleus of V to initiate the monosynaptic stretch reflex.
230
Where do epicritic afferents for fine/discriminative touch project?
The chief sensory nucleus, where they first synapse. They then decussate and travel to the VPM of the thalamus in the trigeminal lemniscus pathway. The VPM projects to the postcentral gyrus.
231
Where do protopathic and epicritic afferents have their cell bodies?
The trigeminal ganglion
232
Where do protopathic afferents for pain and temperature project?
They project to the ipsilateral spinal tract of V, where they first synapse. Second order fibers then decussate to the VPM of the thalamus, traveling in the trigeminothalamic tract. The VMP project to the somatosensory cortex via the posterior limb of the internal capsule
233
Trigeminothalamic tract
The tract that protopathic afferents for pain and temperature take to decussate over and up to the VPM of the thalamus after their first synapse in the ipsilateral spinal tract of V.
234
Trigeminal lemniscus pathway
The tract that epicritic afferents for fine/discriminative touch take to decussate over and up to the VPM of the thalamus after their first synapse in the ipsilateral chief sensory nucleus of V.
235
Which Brodmann's areas does the post-central gyrus include?
Brodmann's areas 3a, 3b, 2, and 1.
236
Where is S2 located, and what does it do?
It is located on the parietal operculum. It is a somatosensory association cortex where further processing of information concerning somesthesis occurs.
237
What does Brodmann Area 3a receive?
Muscle afferents and nociceptive info from the thalamus
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What does Brodmann Area 3b receive?
Cutaneous inputs; tactile perception
239
What does Brodmann Area 1 receive
Most of its stuff is from Area 3b; more detailed information about texture is processed here
240
What does Brodmann Area 2 receive?
Stuff from 3a and 3b, thus this area integrates pain, tactile, and proprioceptive information to allow position and edge detection, size perception, etc.
241
All commands for movement, whether reflexive or voluntary, are ultimately conveyed to the muscles by the activity of the _________
Lower motor neurons, which are the final common pathway for control of movement.
242
What is pre-programmed movement (e.g.: walking, chewing, etc.) a result of? What systems are interacting?
Local circuit input to the lower motor neurons creates the means for pre-programmed movements. These movements can be initiated independently of the brain.
243
Where are the cell bodies of upper motor neurons located?
The brainstem of cerebral cortex
244
Describe the path of the upper motor neurons.
Upper motor axons descend to synapse with the local circuit neurons. Sometimes, they connect to lower motor neurons directly.
245
What do upper motor neuron pathways arising in the cortex do?
They are needed for voluntary movements and for complex spatio-temporal sequences of skilled movements, like fine finger control.
246
Upper motor neurons originating in the brainstem are responsible for what?
Regulating muscle tone, orienting the eyes, head, and body with respect to vestibular, somatic, auditory, and visual sensory information.
247
Upper motor neuron pathways that originate in the primary motor cortex, premotor cortex, and the supplementary cortex are responsible for what?
Planning, initiating, and directing sequences of voluntary movement.
248
What is the third subsystem that controls movement? How does it work?
The cerebellum, which detects the difference or motor error between intended movement and movement actually performed. This leads to real-time and long-term adjustments to movements so that intent and execution eventually align. The cerebellum regulates the activity of upper motor neurons instead of connecting to circuit or lower motor neurons.
249
What is the fourth subsystem that controls movement?
The basal ganglia, which suppress unwanted movement and prepare upper motor neuron circuits for the initiation of movement.
250
What is the definition of a lower motor neuron?
The cell body is located in the central nervous system, and it is projecting its axon into the peripheral nervous system
251
Describe the path of an upper motor neuron
An upper motor neuron of the precentral gyrus sends its axons via the corticospinal tract, or pyramidal tract. The fibers originate from Betz cells in the primary motor cortex, pass through the posterior limb of the internal capsule, and descend in the anterior part of the midbrain. The tract descends as the pyramids in the anterior part of the medulla. About 90% of the fibers decussate at the junction between the brainstem and spinal cord in a place called the pyramidal decussation. Once they decussate, they come to be called the lateral corticospinal tract.
252
Where do upper motor neurons decussate?
In the pyramidal decussation
253
What tract do upper motor neurons take to get from a gyrus down through the brainstem?
The corticospinal tract
254
Where do upper motor axons descending the corticospinal tract synapse?
They synapse in the spinal cord on an anterior horn neuron called the lower motor neuron
255
What is the lateral corticospinal tract?
This is the tract that 90% upper motor neuron axons take after decussating in the pyramidal decussation.
256
What is the anterior corticospinal tract?
This is the tract that 10% of upper motor neuron axons take when they DO NOT decussate in the pyramidal decussation.
257
Do upper motor neuron axons in the lateral corticospinal tract synapse ipsilaterally or bilaterally? What musculature do they innervate?
They synapse ipsilaterally.
They innervate the limb musculature.
258
Do upper motor neuron axons in the anterior corticospinal tract synapse ipsilaterally or bilaterally? What musculature do they innervate?
They synapse bilaterally.
The innervate the axial musculature.
259
In what Rexed laminae are the local circuit neurons located?
Layers VII - VIII
260
In what Rexed laminae are the lower motor neurons located?
Layer IX
261
In the ventral horn, where are lower motor neurons serving the extremities located? What does this mean in regards to the lateral and anterior corticospinal tracts?
They are located laterally in the ventral horn.
This means that the lateral corticospinal tract synapses ipsilaterally with only motor neurons serving distal extremities, like the arm.
262
In the ventral horn, where are lower motor neurons serving the proximal trunk muscles located?
What does this mean in regards to the lateral and anterior corticospinal tracts?
They are located medially in the ventral horn.
This means that the anterior tract synapses bilaterally only with medial motor neurons serving the trunk muscles.
263
How is fine motor control achieved in regards to the number of fibers associated with a motor neuron?
To achieve fine movement, a single motor neuron should innervate only a few muscle fibers.
264
A muscle requires a lot of power. How many fibers are likely associated with one motor neuron innervating that area?
Several thousand fibers per lower motor neuron.
265
Describe fast fatiguable fibers
These fibers produce a large contraction force but fatigue quickly.
266
Describe slow fatigue resistant fibers
Slow fatigue resistant fibers generate small forces that are sustained for long periods without fatigue.
267
Are motor neurons of slow fatigue resistant fibers large or small?
They are small and have fewer fibers associated with them (small ratio of muscle fibers per neuron).
268
Describe features of slow fatigue resistant fibers
They are rich in myoglobin and capillary bed. They have lots of mitochondria and function mostly with aerobic metabolism. They are dark red in color.
269
Describe features of fast fatiguable fibers
Small amount of myoglobin and mitochondria, with a less dense capillary supply that leads to a paler appearance. Anaerobic metabolism. High ratio of muscle fiber : neuron - so there are fewer motor neurons associated with these muscles because each motor neuron is associated with thousands of fibers.
270
What are the three types of muscle fibers?
Fast fatiguable, fast fatigue resistant, and slow fatigue resistant.
271
E.g. of a fast fatiguable muscle
Gastroc muscle, used for rapid, forceful movements like jumping
272
E.g. of a slow fatigue resistant muscle?
Soleus muscle, used to maintain balance as we stand for long periods of time.
273
What sensory organs sense stretch of a muscle, and how do they send information about said stretch?
Muscle spindles send signals via 1a sensory nerves
274
1a sensory nerves
These are afferents sent from the periphery from a muscle spindle when it senses stretch of the muscle. They synapse on an alpha lower motor neuron.
They also synapse on inhibitory interneurons that inhibit the alpha motor neuron of the antagonistic muscle.
275
What is the muscle stretch reflex?
It links a muscle spindle to a lower motor neuron and back to the muscle.
276
Where are the cell bodies of afferent fibers coming from muscle?
Dorsal root ganglion
277
What type of neuron innervates skeletal muscle fibers to form motor units?
Alpha-motor neurons
278
Is excitatory or inhibitory information provided by a muscle afferent to a motor neuron in monosynaptic connections?
Excitatory information
279
What is required for a muscle afferent to have an inhibitory effect on a motor neuron?
An inhibitory interneuron is required, regardless of whether the information is coming from above/below the spinal cord segment in which the motor neuron resides, or the higher motor centers
280
Where can motor neurons receive information from?
From afferents projecting from above or below the spinal cord segment in which the motor neuron resides; INTERNEURON REQUIRED
From higher motor centers; INTERNEURON REQUIRED
From 1a afferents that enter at the spinal segment in which the motor neuron resides
281
When are interneurons required for excitatory stimulation of a motor neuron?
When the afferent fibers project from above or below the segment in which the motor neuron resides, or when the afferent is coming from a higher motor center
282
What type of afferents do muscle spindles produce?
Type Ia and Type II afferent fibers
283
What afferents do Golgi tendon organs give rise to?
Type Ib afferent nerves
284
How does the spindle know when your muscle is being stretched?
The spindle is composed of intrafusal fibers contained in a sheath; the sheath is parallel to extrafusal fibers of the muscle. When the muscle stretches (extrafusal fibers stretch), the parallel intrafusal fibers stretch with them.
285
What are the specialized sensory nerve endings that encircle intrafusal fibers called? What do they do?
These are called annulospiral endings; they are afferent nerves that provide information about the length and changes in length of the muscle fibers associated with the spindle.
They possess membrane channels that are sensitive to mechanical stretch. Upon feeling a stretch, they fire an action potential that travels in a 1a sensory nerve to the dorsal horn, then ventral horn of the spinal cord to reach the alpha motor neuron.
286
Do alpha motor neurons fire an action potential to contract extrafusal or intrafusal fibers of a muscle?
They fire an action potential to contract extrafusal muscle, which by association due to its parallel position, contracts the intrafusal muscle.
287
What motor neuron innervates the muscle spindle? How does it work?
The gamma motor neuron, which fires in concert with the alpha motor neuron, thereby causing simultaneous contraction of the spindle's intrafusal fibers to keep them engaged during times of just general muscle tone.
288
What does the muscle spindle achieve with its separate innervation by a gamma motor neuron?
It can monitor and regulate tone throughout the full extension and flexion of a muscle to create a smooth process of muscle tone.
289
What do Type II afferent nerves from spindle organs do?
These encode muscle fiber length information in the frequency of action potentials. I.e.: increase in length means an increase in APs.
290
What do Type Ia afferent nerves from spindle organs do?
It encodes both length and velocity information in the frequency of its action potentials. I.e.: a rapid increase in fiber length elicits a dramatic increase in action potentials, whereas a less rapid change in fiber length produces a less dramatic change in action potentials
291
What type of connection do Type Ia and II afferent nerves have with their associated motor neuron? What is a motor neuron actually doing?
They have a monosynaptic, excitatory connection, which means that the motor neuron is monitoring the length.
292
What is the purpose of the Golgi tendon organ, and where is it located?
It monitors force and protect the muscles and tendons against generating excessive and potential harmful force. It is located at the junction of the muscle and tendon and connected in series with the muscle/tendon.
293
By which afferents do Golgi tendon organs relay information?
They do so via 1b sensory afferent fibers
294
Where do afferent 1b fibers synapse?
They synapse on inhibitory local circuit neurons (interneurons) in the spinal cord that then inhibit the alpha motor neurons connected to the same muscle as the Golgi tendon organ.
295
What does an excessive muscle contraction cause a Golgi tendon organ to do?
It causes the organ to fire action potentials that inhibit and attenuate the force of the contracting muscle.
296
Explain the path of the Ib afferents of the Golgi tendon organ
The afferent heads to the spinal cord to synapse with an interneuron that has an inhibitory effect on the contracting muscle. At the same damn time, it stimulates an excitatory interneuron to activate the lower motor neuron of the antagonist muscle so that it will contract.
297
What Brodmann areas are contained in the primary somatosensory cortex?
Brodmann areas 1, 2, and 3
298
Where do corticobulbar fibers pass through the internal capsule?
They pass nearest to the genu, or angle of the internal capsule.
299
In terms of medial or lateral, how are leg and arm fibers arranged in the cervical spinal cord (so, after they have decussated)?
The leg/toe fibers are most lateral, and the arm fibers are most medial. Recall that very few trunk fibers decussate, but those that do are located in between the leg and arm fibers.
300
As corticospinal fibers first pass through the internal capsule, what is their general arrangement?
The hand wrist/hand fibers are most anterior and medial, behind them run the upper arm/trunk fibers, behind them, the hip/knee/ankle fibers, and lastly, most posterior and lateral, the toe fibers (so these are the farthest away from the genu). The fibers remain in this organization up to the point where they decussate in the decussation pyramids. Once they cross over, the toe, then leg fibers are again most lateral, but just on the other side of the spinal cord.
301
In a descending corticospinal tract, which fibers are most medial? Why?
The arm fibers are most medial in the spinal cord because they peel off first to synapse on their target motor neuron in the ventral horn, and in the process, get out of the way of corticospinal fibers descending to innervate the legs.
302
Where does the vestibulospinal tract terminate, and what does it do?
It terminates at the cervical and thoracic spinal cord levels to innervate neck and trunk muscles to control their coordinated movements.
303
Reticulospinal tract - where does it terminate, and what does it do?
These fibers originate in the reticular system of the brainstem and terminate at the thoracic and cervical spinal cord level to innervate neck and trunk muscles to control coordinated movements of the head and trunk.
304
The rubrospinal tract
Originates in the red nucleus of the brainstem and participates in the control of arm muscles.
305
The colliculospinal tract
Originate in the superior colliculus and terminates at the cervical spinal cord level to innervate neck muscles to coordinate head and eye movements.
306
A brain lesion to the precentral gyrus/motor cortex, the posterior limb of the internal capsule, or just above the pyramidal decussation would cause what?
Weakness of the contralateral face and limbs
307
If a patient presented with right-sided weakness of the face and limbs after experiencing head trauma in an accident, what might be on your differential as far as damaged structures within the brain are concerned?
A left brain lesion to the precentral gyrus/motor cortex, the posterior limb of the internal capsule, or just above the pyramidal decussation.
308
A lesion occurring below the pyramidal decussation (structure involved with the corticospinal tract), along the lateral corticospinal tract high in the cervical spinal cord would lead to what kind of presentation?
The patient would present with ipsilateral arm and leg weakness
309
If a patient is presenting with right-sided arm and leg weakness after a spinal cord injury, on which side of the spinal cord did the lesion occur?
The right side
310
A lesion occurring below the pyramidal decussation (structure associated with the corticospinal tract) along the lateral corticospinal tract below the cervical spinal cord would lead to what kind of presentation?
Ipsilateral leg weakness
311
A patient presenting with only left-sided leg weakness after a spinal cord injury may have a lesion where?
A lesion of the left side of the spinal cord, somewhere along the corticospinal tract, below the cervical spine.
312
A patient presents with left-sided arm and leg weakness after a spinal cord injury. Where is the lesion?
On the left-side of the spinal cord, high in the cervical spine, somewhere along the corticospinal tract.
313
What is the result of a lesion of ventral horn cells in regards to muscle integrity?
The patient would present with weakness of the ipsilateral limb served by that lower motor neuron population or peripheral nerve.
314
Where does muscle weakness indicate a possible lesion?
To either an upper or lower motor neuron
315
How do upper motor neurons control lower motor neuron reflex arcs? What is the result when this action is interrupted?
Upper motor neurons usually influence lower motor neurons by inhibiting the local reflex arcs. When lesions to the upper motor neuron or corticospinal tract interrupt the inhibition, the local spinal reflex systems become hyperactive.
316
How would a lesion to a lower motor neuron or peripheral nerve affect muscles and trophic relationships?
Muscle tone and muscle stretch reflexes would be decreased.
Trophic substances from nerves would not be able to reach their intended/innervated muscles, leading to their atrophy.
317
Loss of lower motor neuron input to muscles leads to ________ and may spontaneously discharge, creating contractions of small muscle groups called _________.
Hyperexcitability
Fasciculations
318
What produces the Babinski sign?
An upper motor neuron lesion
