Module 2 Flashcards
Rostral (Anterior)
Toward the nose
Caudal (posterior)
Toward the tail (or rear)
Dorsal (superficial)
Toward the back
Ventral (inferior)
Toward the belly
Medial
Toward the midline
Lateral
Toward the side
What makes up the central nervous system?
Consists of the cerebrum, cerebellum, brainstem and spinal cord
What are the two divisions of the peripheral nervous system?
1) Somatic (voluntary)
2) Visceral (autonomic)
Which is the dorsal side of the brain?
The top
Dura Mater
“Hard mother”
The leathery membrane encasing the brain and spinal cord. On the exterior it is anchored to the cranium and interior to the pia.
Pia mater
“Soft mother”
A film of connective tissue supplied with capillaries that nourish the brain.
Arachnoid
“Spidery”
A network between the dura and pia that is richly vascularized. It is attached to the dura on one side and the pia on the other. Contains the sub arachnoid space. This area acts like a shock absorber to protect the brain from mechanical damage.
Sub Arachnoid Space
The space between the pia mater and archnoid filled with cerebro-spinal fluid that adds to the shock absorbind effect of the arachnoid layer.
Ventricles
Brain spaces filled with cerebral spinal fluid.
Four major divisions of the central nervous system
1) Prosencephalon Forebrain
2) Mesencephalon Midbrain
3) Rhombencephalon Hindbrain
4) Spinal cord
Prosencephalon Forebrain division(s)
1) Telencephalon
2) Diencephalon
Telencephalon
Cerebral cortex, basal ganglia, etc.
Diencephalon
Thalamus, hypothalamus, etc.
Mesencephalon Midbrain division(s)
1) Mesencephalon
Mesencephalon
Tectum, etc.
Rhombencephalon Hindbrain division(s)
1) Metencephalon
2) Myelencephalon
Metencephalon
Cerebellum, pons, etc.
Myelencephalon
Medulla oblongata, etc.
Hemisphere
Half a sphere.
- In cerebral cortex there is a right and left hemisphere
Cortex
Rind, usually cortical structures are organized into layers.
-Ex: Cerebral cortex and cerebellar cortex
Lobe
A chunk of cortex separated from the next chunk by a deep groove.
Gyrus
A ridge in the brain
Sulcus
A groove
Fissure
A deep sulcus - sometimes used interchangeably with sulcus.
Piriform Cortex (paleocortex)
Smooth cortex that makes up the olfactory bulbs. We think this is where the other cortex came from.
Put the three types of cortex in order from oldest (1) to newest (3)
1) Paleocortex
2) Archicortex
3) Neocortex
Grey matter
Matter in the nervous system made up of cell bodies
White matter
Matter in the nervous system made up of myelinated axons (fibers)
Nuclei
Roughly circumscribed groups of cell bodies
Fascicles
Bundles of fibers
Peduncles
Thick bundles of fibers that connect big parts of the brain to other big parts of the brain.
Coronal
A slice of the brain taken like a crown across the top of the head.
Horizontal
A slice of the brain that cuts horizontally across the head.
Sagittal
A slice of the brain taken in a plane that goes straight into your nose (where you might put a plane of symmetry on the face)
Victor Horsley
Horsley designed a machine that used landmarks on the skull (bony ridges and hollows) as reference points to create a coordiante system to navigate the brain so that each point in the brain had its own unique set of coordinates.
Key words: stereotaxic apparatus
Talairach coordinate system
The mostly commonly used coordinate system for navigating the brain today.
- Conceptually similar to Stereotaxic system
- Reference point is a structure inside the head which can be visualized using MRI
Phrenology
A completley wrong view that used to be held that we could see localization of faculties based on the features of the skull
Phineas Gage
When Phineas Gage suffered a severe wound through the front of his brain, it completely changed his personality and ability to maintain social interactions and normality. This showed the localization of executive function to the prefrontal lobes.
Broca’s area
A region in the left inferior frontal lobe which deals with the ability to speak.
Wernicke’s area
An area in the superior temporal lobe that is correlated with the ability to recognize words.
Wilder Penfield
Discovered the motor homunculus by stimulating the brains of patients during surgery.
Motor homonculus
A map of the body laid out over a specific region of the brain.
HM
Shows localization of functions that form memories.
- Had his hippocampus removed and he couldn’t remember anything new but retained all old memories
Pituitary Gland
Gland that secretes hormones and is regulated by the hypothalamus.
Hypothalamus
Many nuclei involved in motivated behaviors and more
Thalamus
Many thalmic nuclei relay informaiotn about the senses to the cortex.
Basal Ganglia
A group of nuclei involved with motor function
- Caudate
- Putamen
- Globulus pallidus
- Substantia nigra
Three layers of the spinal cord starting from the top near the base of the brain
1) Cervical
2) Thoracic
3) Lumbar
4) Sacral
Cytoarchitecture
The use of microscopy to look at the cellular arrangements in different slices of the brain to identify different parts of the brain.
Brodmann Areas
The name given to the different areas that Brodmann classified using cytoarchitecture. They correlate with different functions.
Santiago Ramon y Cajal
Developed a staining method that allowed us to visualize a single neuron where we never could before.
Which has more dense branching, excitatory cells or inhibitory cells?
Inhibitory
Eadwaerd Muybridge
Scientist who used an electronic timing device to record photographs of subjects moving from all angles to better study the aspects of movement that are not entirely obvious with the naked eye.
- Subjects moved in front of a black wall with white string hung to create a “graph paper” of sorts behind them.
- Resulted in as many as 36 negatives
Descending systems (upper motor neurons)
Neural systems that operate from the top down.
1) Motor cortex: Planning, initiating and directing voluntary movements.
- Synapsed on by basal ganglia
2) Brainstem centers: Basic movements and postural control.
- Synapsed on by cerebellum
- These feed directly into the spinal cord and brainstem circuits and thus to lower motor neurons
Spinal Cord and Brainstem Circuits
1) Local circuit neurons: Lower motor neuron integration
- Synapses on motor neuron pools and is synapsed on by sensory inputs
2) Motor neuron pools: Lower motor neurons
- Synapses onto muscles
Dorsal Horn
Part of the spinal cord where inputs from sensory cells collect and which is made of the somas of local circuit neurons
Dorsal root ganglia
A portion of the spinal cord that contains somas of sensory neurons whose axons travel out to peripheral sensory receptors and into the cord.
AFFERENT
Afferent
Going in (arrives)
Efferent
Going out
Lateral white matter in the spinal cord
Carries fibers (axons) from the motor cortex
Ventral horn
A portion of the spinal cord made of the somas of lower motor neurons.
Ventral roots
A portion of the spinal cord that contains the axons of lower motor neurons that travel out towards muscles.
EFFERENT
Medial white matter in the spinal cord
Carries fibers from the brainstem
Dorsal root fibers (list from largest to smallest)
1) Ia, II: Muscle spindles
2) Ib: Golgie tendon organs
3) Beta: Tactile
4) Delta: Sharp pain/temp
5) C: Dull pain
Ventral roots (list from largest to smallest)
1) Alpha; Alpha-motorneuron
2) Gamma: Gamma-motorneuron
Motor unit
The group of muscle fibers that receive input from a single motor neuron.
- If one motor neuron innervates 100 fibers then the motor unit is all 100
How many synapses exist on each muscle fiber
1!!! One neuron can synapse onto multiple muscle fibers, but only one synapse is on each muscle fiber.
Somatotopic arrangement of lower motor neurons
This refers to the concept that motor neurons that innervate proximal muscles are medial and those that innervate distal muscles are lateral.
- There is a map of the muscles on the spinal cord so that proximal muscles are toward the center of the cord and distal muscles are toward the edge of the spinal cord.
S alpha motor nuerons
(Slow)
Smaller motor neurons that conduct slowly. They innervate muscle fibers that generate small, lasting contractions (posture, etc.).
- Will be stimulated many times and don’t get fatigued
FF alpha motor neurons
(Fast Fatigue)
Larger than S alpha motor neurons, these neurons innervate large groups of muscles that generate large forces (ie. jumping)
- Will die down and be “fatigued” very quickly
FR alpha motor neurons
(Fatigue Resistant)
Alpha motor neurons that innervate muscles with intermediate properties.
- Can stimulate rapidly and it will hold for a while, but eventually dies down (after FF would but before S would)
Size of motor units and specificity of movement
In general, small motor units are involved in fine movements and large motor units are involved in more coarse movements.
Motor pool
The group of motor neurons that innervate a single muscle.
- Can comprise more than one type of motor unit!
- Ex. Leg muscle might have different types of motor units for standing, walking and jumping
Intrafusal fibers
Muscle fibers that are arranged in parallel with extrafusal fibers
Nuclear bag fibers
Muscle fibers that are sensitive to the rate of change in muscle length (velocity) and wrap around the intrafusal muscle fibers
Nuclear chain fibers
Muscle fibers that are sensitive to muscle length and wrap around intrafusal muscle fibers
Group Ia sensory afferents
Muscle fiber that wrap around the bag AND chain fibers so it is most active when muscle length is changing (ie. muscle is stretching)
Group II sensory afferents
Muscle fibers that wrap around the chain fibers only and are most active when the muscle is stretched.
Gamma motor neurons
Motor neurons that innervate intrafusal fibers.
- Regulate the sensitivity of the muscle spindle by pulling at both ends of the bag and chain fibers, thereby stretching the regions where the afferent endings are wrapped
- This stretching effectively makes the muscle fiber more sensitive to length
Golgi Tendon Organs
Capsules encasing group Ib afferents that wrap around collagen fibrils to send signals about the state of the muscle.
- Embedded in the tendons that connect muscle to bone
- Signal information about force
- *Most active when the muscle contracts
Monosynaptic Stretch Reflex
The patellar reflex induced by a hammer to a knee is some check-ups.
- Excitatory, so in order to inhibit have to lessen excitatory input, not create inhibitory action
- Agonist muscle is stretched, which leads to an increase in discharge by 1a afferents
- Discharge leads to monosynaptic excitation of the alpha motorneuron in the lateral horn that innervates the same muscle and leads to a contraction to restore muscle length
- Discharge also leads to a disynaptic relaxation of the antagonist. The 1a afferent synapses with an inhibitory inerneuron in the dorsal horn that suppresses activity in the alpha motorneuron that innervates the antagonist.
- NOTE: 1a fibers and alpha motorneurons have large diameters and conduct quickly –> fast
Golgi tendon organ reflex
A reflex that maintains tension via negative feedback
1) The agonist contracts, muscle tension increases and 1b afferents fire hard
2) The 1b afferent synapses with an inhibitory interneuron that reduces firing of the alpha motorneurno
3) The muscle relaxes and tension decreases
Betz cells
Really big cells with stout axons that form most fibers in the descending (corticospinal and corticobulbar) and are thus examples of upper motor neurons.
- Gives the greatest sensitivity and acuity in the smallest cortex space
Corticospinal
Descending motor tract that originates in the motor and premotor cortices and ends in the spinal cord
- Crosses at the midline
Corticobulbar
Descending motor tract that originates in the motor and premotor cortices and ends in the brainstem.
- Uncrossed
Lateral-cortico spinal tract
Comprises most of the cortico-spinal tract and originates from the premotor cortex and the primary motor cortex.
- Most fibers cross at the pyramidal decussation (medulla) and terminate on lateral motor neurons including those that move distal muscles like fingers and toes
Anterior (ventral) cortico spinal tract
Crosses the cord and makes bilateral and postynaptic connections with medial motorneurons that are used to maintain posture.
Supplementary and Premotor Cortex
Cortices responsible for movement planning.
Motor cortex
Cortex responsible for movement execution.
Functional organization of the motor cortex
As with all cortices, cells are arranged in columns that perform common functions.
- We currently believe that these columns are grouped by common movement, not target muscle
Components of striatum
1) Caudate
2) Putamen
Components of globus pallidus (Palladum)
1) Pars externa
2) Pars interna
Components of substantia nigra
1) Pars compacta
2) Pars reticulata
Medium spiny neurons
- Receive many excitatory cortical inputs, though each input contributes little
- Silent unless excited
- Gabergic
Globus pallidus or substantia nigra pars reticulata neuron
- Active unless inhibited
- Gabergic
Dopaminergic neurons
Neurons in the basal ganglia that excite some medium spiny cells and inhibit others.
Examples of non-motor loops in the basal ganglia
- Executive/prefrontal loop
- Limbic loop - involved with conditions like obsessive compulsive disorder and Tourette’s
- Oculomotor loop
Two major loops in the basal ganglia
1) Non-motor loops
2) Motor loops
Two main motor pathways of the motor loop
Motor loop regulates the upper motor neurons that initiate and help coordinate voluntary movement
1) Direct pathway
2) Indirect pathway
Direct pathway
The motor pathway that accelerates movement by disinhibiting the thalamus and hence the upper motor neurons in the cortex.
- Associated with Huntington’s disease
- Removing dopamine has a “take the foot off the accelerator” effect
Indirect pathway
The motor pathway that brakes movement by modulating disinhibitory actions of the direct pathway.
- Associated with Parkinson’s
- Removing dopamine has a “step harder on the brake” effect
What role does dopamine play in the direct and indirect pathways?
Dopamine excites the direct pathway via D1 receptors and inhibits the indirect pathway via D2 receptors. Overall, this is a net excitatory effect.
Hyperkinesia
Diseases associated with over-excitation and inability to control movements.
- Hemiballismus
- Huntington’s Disease
Hemiballismus
A type of hyperkinesia associated with loss of the subthalamic nucleus.
- Indirect pathway, so activity in the globus pallidus internal is reduced so the VA/VL thalamus is not inhibited enough and overexcites the cortex
Huntington’s Disease
A type of hyperkinesia associated with loss of the striatum.
- Genetic disorder
- Chorea: Involuntary movements
- Severe movement disorder
- Akinesia - patient can hear and understand but not speak
- Loss of putamen’s inhibitory effects –> increased cortical activity
Hypokinesia
Diseases associated with the loss of the substantia nigra pars compacta and over-inhibition.
- Parkinson’s disease
- Drug induced
Parkinson’s Disease
A type of hypokinesia associated with unbalanced dopamine levels due to loss of the substantis nigra pars compacta.
- Bradykinesia (slowed, impaired movement)
- Rigidity
- “Pill rolling” tremor
Therapies for Parkinson’s
- L-Dopa
- Thalamotomy and pallidotomy
- Deep brain stimulation of the subthalamic nucleus for example
- Implantation of fetal dopaminergic neurons
- Optically gated ion channels in damaged neurons (Same as Dickman’s presentation but this is used as therapy, not research)
6 muscles that control eye movement
1) Superior rectus
2) Inferior rectus
3) Lateral rectus
4) Medial rectus
5) Superior oblique
6) Inferior oblique
How is the superior oblique muscle innervated?
The super oblique muscle is innervated from the trochlear nucleus in the caudal midbrain by the cranial nerve IV BILATERALLY!
How is the lateral rectus innervated?
The lateral rectus is innervated by from the abducens nucleus in the pons by cranial nerve VI IPSILATERALLY!
How are the superior and inferior rectus, inferior oblique and medial rectus muscle innervated?
These muscles are innervated from the oculomotor nucleus in the midbrain through cranial nerve III.
Three types of eye movements
1) Those that direct gaze to targets of interest or track those targets as they move
2) Those that help align the fovea of each eye on the target of interest when the distances between each eye and target are different.
3) Movements that compensate for head movements to keep the target of interest centered on the fovea.
Saccades
Jerky movements that direct the gaze to targets or track them as they move.
- Associated with sudden change in place so the eyes have to catch up to where the object is- once they find it they are locked in and can follow it smoothly
What’s so special about the superior colliculus?
There is a map of visual space on the superior colliculus. so that if you electrically stimulate any given point on the map the eyes will move toward that position.
Parinaud syndrome
Aka dorsal midbrain syndrome.
- Syndrome caused by a tumor of the pineal gland that compresses the superior colliculi and results in paralysis of upward gaze.
PPRF
The horizontal gaze center which controls the lateral and medial rectus muscles by connecting the midbrain (medial rectus) to the pons (later rectus) to control horizontal eye movement by relaxing and contracting antagonist pairs.
Effects of lesions to the frontal eye fields or superior colliculus
One but not the other: Temporary loss of ability to make saccades (because the brain will learn to compensate)
Superior colliculus: Impedes ability to make fast saccades
Frontal eye fields: Impedes the ability to make voluntary movements away from a salient stimulus in the visual field or movements toward “remembered” positions.
Both: Permanent loss of ability to make saccades.
Preganglionic (visceral motor systems)
Lies within the CNS and output goes to the ganglia.
- Cholinergic via nicotinic receptors
Postganglionic (visceral motor systems)
Lies in the PNS and output goes to effectors (muscles, glands, organs, etc.)
- Sympathetic: Noradrenergic
- Parasympathetic: Cholinergic via muscarinic receptors (mediated by G proteins)
Sympathetic Nervous System
Fight or Flight
- Preganglionic cells lie in the lateral horn (thoracic and lumbar regions of the spinal cord)
- Exit via the ventral root
- Tonically active
- Reach the sympathetic chain ganglia via the white communicating rami - Some ganglion cells in the sympathetic trunk (just outside the spinal cord- para vertebral) and the other are tucked between the spinal cord and the effector organs
- Postganglionic are unmyelinated and send axons via the gray communicating rami or through branches to meet effectors
White communicating rami
The means by which sympathetic preganglionic cells reach the sympathetic chain ganglia
Gray communicating rami
The pathway through which postganglionic cells in the sympathetic nervous system send their axons
