Exam 4 Nervous System Flashcards
Synapse
Site of communication between two or more neurons or between a neuron and another cell
Types of Synapses
Electrical and Chemical
Electrical Synapse
Structure - Gap junction formed between pre and post synaptic membranes. Protein pores permit ions to pass between cells.
Function - Membrane potential passes from cell to cell
Examples - Intercalated discs in cardiac muscle or gap junctions in smooth muscle
Presynaptic Membrane
The neuron that passes the impulse to another neuron
Postsynaptic Membrane
The neuron receiving the signal or impulse
Excitatory Neurotransmitter
Cause depolarization and promote the generation of action potentials
Inhibitory Neurotransmitter
Causes hyperpolarization and suppress the generation of action potentials
Chemical Synapse
All synapses and communications between neurons involve neurotransmitters
Chemical Conduction at the Synapse
There is a space (synaptic cleft) between the axon terminal and the adjacent neuron. As the action potential reaches the end of the axon, a chemical is released that travels across the synaptic cleft to the next neuron to alter its electric potential
Acetylcholine
Primarily direct, through binding to chemically gated channels
In the PNS - Plays a role in skeletal muscle movement, as well as in the regulation of smooth muscle and cardiac muscle
In the CNS - Involved in learning, memory, and mood
Norepinephrine
Widely distributed in the brain and in portions of the ANS
Typically has an excitatory, depolarizing effect on the postsynaptic membrane, but the mechanism is quite distinct from that of ACh
Dopamine
Has both inhibitory and excitatory areas of the brain
Inhibitory effects has an important role in our precise control of movements
Excitatory effects - Cocaine inhibits the removal of dopamine from synapses in specific areas of the brain. The resulting rise in dopamine concentrations at these synapses is responsible for the “high” experienced by cocaine users
Serotonin
Inadequate serotonin production can have effects on a person’s attention and emotional states and may be responsible for many cases of severe chronic depression.
Antidepressant drugs inhibit the reabsorption of serotonin by axon terminals. This inhibition leads to increased serotonin concentrations at synapses, and over time, the increase may relieve the symptoms of depression.
GABA
Gamma-aminobutryic acid
Has an inhibitory effect; GABA release in the CNS appears to reduce anxiety and some antianxiety drugs work by enhancing this effect.
Neuromodulators
A compound released by a neuron that affects the sensitivity of another neuron to a neurotransmitter
Examples: Opoids such as endorphins
Actions of a Neuromodulator
Alters rate of release of neuromodulators
Bind receptor on neuron and activate enzymes
EPSP
Excitatory Postsynaptic Potential
Graded depolarization caused by the arrival of a neurotransmitter at the postsynaptic membrane
IPSP
Inhibitory Postsynaptic Potential
Graded hyperpolarization of the postsynaptic membrane. the neuron is said to be inhibited because a larger than usual depolarizing stimulus is needed to bring the membrane potential to threshold.
Postsynaptic Potentials
Graded potentials that develop in the postsynaptic membrane in response to a neurotransmitter
Temporal Summation
The addition of stimuli occurring in rapid succession t a single synapse that is active repeatedly.
This form of summation can be likened to using a bucket to fill up a bathtub: You can’t fill the tub with a single bucket of water but you will fill it eventually if you keep repeating the process.
Spatial Summation
Occurs when simultaneous stimuli applied at different locations have a cumulative effect on the membrane potential.
You could fill a bathtub immediately if 50 friends emptied their bucket into it all at the same time.
Presynaptic Inhibition
Inhibition that reduces the amount of neurotransmitter released when the action potential arrives there, and thus reduces the effects of synaptic activity on the postsynaptic membrane.
Presynaptic Facilitation
Activity at an axoaxonic synapse increases the amount of neurotransmitter released when an action potential arrives at the axon terminal.
Principles of Synaptic Transmission
- Unidirectional
- Susceptible to fatigue
- Susceptible to drugs and medications
- Oxygen consumption
- Summation occurs
Neuronal Pools
Functional groups of neurons that integrate incoming information from receptors which then forward processed information to other designations
Diverging Circuit
Spread of information from one neuron to several neurons, or from one pool to multiple pools
Converging Circuit
A mechanism for providing input to a single neuron from multiple sources
Serial Processing
Information is relayed in a stepwise fashion, from one neuron to another or from one neuronal pool to the next
Parallel Processing
Occurs when several neurons or neuronal pools process the same information simultaneously
Divergence must take place before parallel processing can occur
Reverberation
Collateral branches of axons somewhere along the circuit extend back toward the source of an impulse and further stimulate the presynaptic neurons.
Length of Spinal Cord
Approximately 45 cm (18 in) long, with a maximum width of roughly 14 mm.
Segments of the Spinal Cord
- Cervical enlargement
- Lumbar enlargement
Cervical Enlargement
Supplies nerves to the shoulder and upper limbs
Lumbar Enlargement
Provides innervation to structures of the pelvis and lower limbs
Conus medularis
Inferior to the lumbar enlargement the spinal cord becomes tapered and conical.
Dorsal Root Ganglia
Located near the spinal cord, every spinal cord segment is associated with a pair of these; these ganglia contain the cell bodies of sensory neurons
Dorsal Root
Axons of the neurons form the dorsal root, which bring sensory information into the spinal cord
Ventral Roots
A pair of ventral roots contains the axons of motor neurons that extend into the periphery to control somatic and visceral effectors.
Spinal Nerve
Distal to each dorsal root ganglion
The sensory and motor root are bound together into a single spinal nerve
Contain both afferent and efferent fibers
31 pairs of spinal nerves
Gray Matter
Integrates information and initiates commands
Dominated by the cell bodies of neurons, neuroglia, and unmyelinated axons
White Matter
Carries information from place to place
Contains large numbers of myelinated and unmyelinated axons
Gray Commisures
Posterior to and anterior to the central canal contain axons that cross from one side of the cord to the other before they reach an area in the gray matter
Anterior Gray Horns
Contain somatic motor nuclei
Posterior Gray Horns
Contain somatic and visceral sensory nuclei
Lateral Gray Horns
Located only in the throacic and lumber segments and contain visceral motor nuclei
Anterior White Columns
Lie between the anterior gray horns and the anterior median fissure
Interconnected by the anterior white commissure
Anterior White Commissure
A region where axons can cross from one side of the spinal cord to the other
Lateral White Columns
The white matter between the anterior and posterior columns on each side makes up the lateral white column
Posterior White Columns
Lie between the posterior gray horns and the posterior median sulcus
Spinal Meninges
A series of specialized membranes surrounding the spinal cord, provide the necessary physical stability and shock absorption
Dura Mater
Layer that forms the outermot covering of the spinal cord
Contains dense collagent fibers that are oriented along the longitudinal axis of the cord
Arachnoid Mater
The middle meningeal layer
The inner surface of the dura mater and the outer surface of the arachnoid mater are covered by simple squamous epithelia
Pia Mater
The innermost meningeal layer
Consists of a meshwork of elastic and collagen fibers that is firmly bound to the underlying neural tissue
Epineurium
Outermost layer of the nerve
Perineurium
Middle layer of the nerve
Separate adjacent bundles of nerve fibers in a peripheral nerve
Endoneurium
Inner layer of the nerve
Surround individual nerve fibers
Plexuses
Interlacing of nerves from which other nerves arise; all white matter
Cervical Plexus
C1-C5; Innervates the muscles of the neck and extend into the thoracic cavity
Brachial Plexus
C5-T1; Innervates the pectoral girdle and upper limb
Lumbar Plexus
L1-L4; Primarily deals with movement of the hip or upper leg
Sacral Plexus
L4-S4
Reflex Arc
Impulse arrives at the cell and activates the receptor. The receptor activates the sensory neuron which carries information to the CNS. The integrator integrates information for the motor neuron to carry. The motor neuron tells the neurotransmitters to release. The peripheral effector responds to this release which, for example, would pull your hand away from the tack.
Innate Reflex
Results from the connections that form between neurons during development
Genetically determined
Acquired Reflex
Learned motor patterns; developed
Somatic Reflex
Control skeletal muscle contractions
Include superficial and stretch reflexes
Visceral Reflex
Control actions of smooth and cardiac muscles, glands, and adipose tissue
Monosynaptic Reflex
One synapse; involve the simplest reflex arc
Polysynaptic Reflex
Multiple synapses; longer delay between stimulus and response which has to do with the amount of synapses involved
Example of Stretch Reflex
Automatically regulates skeletal muscle length
“Knee-jerk” or patellar reflex - when a physician taps your patellar tendon with a reflex hammer, receptors in the quadriceps muscle are stretched. The distortion of the receptors in turn stimulates sensory neurons that extend into the spinal cord, where they synapse on motor neurons that control the motor units in the stretched muscle. This leads to a reflexive contraction of the stretched muscle that extends the knee in a brief kick.
Tendon Reflex
Monitors the external tension produced during a muscular contraction and prevents tearing or breaking of the tendons.
Withdrawal Reflex
Move affected parts of the body away from a stimulus. Painful stimuli trigger the strongest withdrawal reflexes, but these reflexes are sometimes initiated by the stimulation of touch receptors or pressure receptors.
Crossed Extensor Reflex
Involves a contralateral reflex arc because the motor response occurs on the side opposite the stimulus
Reinforcement
An enhancement of spinal reflexes by stimulating excitatory neurons in brain stem or spinal cord creating EPSPs at reflex motor neurons facilitating postsynaptic neurons
Spinal Shock
Loss of all neurological activity below the level of injury
Decerebrate Rigidity
Caused by extensive damage to the brainstem; There is head extension with body arched, the arms are extended, adducted, and pronated; the legs are extended with plantar flexion of the feet
Ventricular System of the Brain
Set of communicating cavities within the brain; these structures are responsible for the production, transport and removal of cerebrospinal fluid.
Lateral Ventricles
Located within their respective hemisphere of the cerebrum; they have horns which project into the frontal, occipital, and temporal lobes. The volume of the lateral ventricles increases with age.
Third Ventricle
The lateral ventricles are connected to the third ventricle by the foramen of Monro.
Situated in between the right and left thalamus. The anterior surface of the ventricle contains two protrusions - supraoptic recess and infundibuar recess)
Fourth Ventricle
Receives CSF from the third ventricle via the cerebral aqueduct; it lies within the brainstem, at the junction between the pons and medulla oblongata.
Function of Cerebrospinal Fluid
Protection - acts as a cushion of the brain
Buoyancy - net weight of brain is reduced to 25 grams and it prevents excessive pressure on the base of the brain
Transports nutrients, chemical messengers, and waste products.
Formation of Cerebrospinal Fluid
Choroid plexus - an area within each ventricle that produces CSF
Produced from arterial blood by the choroid plexuses of the lateral and fourth ventricles by a combined process of diffusion, pinocytosis, and active transfer. A small amount is also produced by ependymal cells.
Circulation of Cerebrospinal Fluid
Choroid plexus secretes the CSF into the lateral ventricle, then it travels to the third ventricle by the intraventricle foramen. From there it moves to the 4th ventricle through the cerebral aqueduct.
Medulla Oblongata Location
Lowest part of the brainstem
Medulla Oblongata Functions
Carries out and regulates life sustaining functions such as breathing, swallowing, and heart rate.
Reticular Formation
Loosely organized mass of gray matter that contains embedded nuclei. It extends from the medulla oblongata to the midbrain.
Reflex Centers
Receive inputs from cranial nerves, the cerebral cortex, and the brain stem.
2 Major Groups - cardiovascular centers and respiratory rhythmicity centers
Cardiovascular Centers
Adjust heart rate, the strength of cardiac contraction, and the flow of blood through peripheral tissues
Respiratory Rhythmicity Centers
Set the basic pace for respiratory movements; their activity is regulated by input from the apnuestic and pnuemotaxic respiratory centers of the pons.
Autonomic Nuclei of Medulla Oblongata
Nuclei located in the spinal cord and brainstem from which general visceral efferent preganglionic fibers arise
Cranial Nerve Nuclei of Medulla Oblongata
The medulla oblongata contains sensory and motor nuclei associated with five of the cranial nerves (8, 9, 10, 11, and 12)
Relay Stations Along Sensory and Motor Pathways in the Medulla Oblongata
The nucleus gracilis and nucleus cuneatus pass somatic sensory information to the thalamus
Decussation
Tracts leaving the brain stem nuclei cross over to the opposite side of the brain before reaching their destination
Site of crossover is called the decussation of pyramids
Pons Location
Area of the hindbrain that sits directly above the medulla
Pons Function
Connects the cerebellum with the midbrain diencephalon, cerebrum, and spinal cord
Cranial Nerve Nuclei in Pons
These cranial nerves (5, 6, 7, and 8) innervate the jaw muscles, the anterior surface of the face, one of the extrinsic eye muscles, and the sense organs of the internal ear.
Respiratory Centers in the Pons
On each side of the pons, the reticular formation in this region contains two respiratory centers: the apneustic center and the pneumotoxic center
These centers modify the activity of the respiratory rhythmicity centers in the medulla oblongata
Relay Centers and Pathway in Pons
The pons links the cerebellum with the brain stem, cerebrum, and spinal cord
Cerebellum Location
Lower area of the brain, directly behind/below the pons
Cerebellum Functions
Responsible for balance and coordination of muscles and the body
White Matter of the Cerebellum
Arbor vitae and cerebellar peduncles
Arbor vitae
“Tree of Life”
Connects the cerebellar cortex and nuclei with the cerebellar peduncles
Superior Cerebellar Peduncles
Link the cerebellum with nuclei in the midbrain, diencephalon, and cerebrum
Middle Cerebellar Peduncle
Connected to a broad band of fibers that cross the ventral surface of the pons at right angles to the axis of the brain stem.
Also connect the cerebellar hemisphere with sensory and motor nuclei in the pons
Inferior Cerebellar Peduncles
Communicate between the cerebellum and nuclei in the medulla oblongata and carry ascending and descending cerebellar tracts from the spinal cord
Gray Matter in the Cerebellum
Cerebellar cortex and cerebellar nuclei
Cerebellar Cortex
Outermost layer of the brain; made up of tightly packed neurons
Divided into four different lobes: temporal, occipital, frontal, parietal
Cerebellar Nuclei
Embedded within the arbor vitae
Midbrain Location
Sits on top of the pons
Midbrain Function
Regulates auditory and visual reflexes and controls alertness
Tectum
Roof of the midbrain
Superior colliculi
Receives visual inputs from the lateral geniculate nucleus of the thalamus on that side
Inferior colliculi
Receives auditory input from nuclei in the medulla oblongata and pons
Red Nuclei
Contains numerous blood vesses, which give it a rich red color; this nucleus receives information from the cerebrum and cerebellum and issues subconscious motor commands that affect upper limb position and background muscle tone
Substantia Nigra
The largest midbrain nucleus; it lies lateral to the red nucleus
Inhibits activity of the basal nuclei in the cerebrum
Cranial Nerve Nuclei in the Midbrain
Nuclei associated with cranial nerves 3 and 4
Thalamus
On each side of the diencephalon; the thalamus is the final relay point for sensory information ascending to the primary sensory cortex
It acts as a filter, passing on only a small portion of the arriving sensory information
Also coordinates the activites of the basal nuclei and the cerebral cortex by relaying information between them
Thalamic Nuclei
Deals primarily with the relay of sensory information to the basal nuclei and cerebral cortex
Anterior Nuclei of Thalamus
Part of the limbic system; this system is involved with emotion and motivation
Medial Group Nuclei of the Thalamus
Provide an awareness of emotional states by connecting emotional centers in the hypothalamus with the frontal lobes of the cerebral hemispheres
Ventral Group Nuclei of the Thalamus
Relays information from the basal nuclei of the cerebrum and the cerebellum to somatic motor areas of the cerebral cortex
Posterior Group Nuclei of the the Thalamus
Pulvinar nuclei - integrate sensory information projection to the cerebral cortex
Lateral geniculate nucleus - receives visual information over the optic tract, which originates at the eyes
Medial geniculate nucleus - relays auditory information to the appropriate area of the cerebral cortex from specialized receptors of the internal ear
Lateral Group Nuclei in the Thalamus
Form feedback loops with the limbic system and the parietal lobs of the cerebral hemispheres
Affects emotional states and the integration of sensory information
Hypothalamus
Extends from the area superior to the optic chiasm, a crossover where the optic tracts from the eyes arrive at the brain, to the posterior margins of the mammillary bodies
Functions of the Hypothalamus
- Subconscious control of skeletal muscle contractions
- Control of autonomic function - adjusts and coordinates the activities of autonomic centers in the pons and medulla oblongata that regulate heart rate, blood pressure, respiration, and digestive functions
- Regulation of endocrine system
- Secretion of antidiuretic hormone and oxytocin
- Regulates subconscious motor activity
Limbic System
Includes nuclei and tracts along the border between the cerebrum and diencephalon
Functional group rather than anatomical group
Functions of Limbic System
- Establishing emotional states
- Linking the conscious, intellectual functions of the cerebral cortex with the unconscious and autonomic functions of the brain stem
- Facilitating memory storage and retrieval
Components of the Limbic System
- Cortical
- Diencephalon
- Reticular formation
Cerebrum
The largest region of the brain, contains motor, sensory, and association areas
Conscious thoughts and all intellectual functions originate in the cerebral hemispheres
Basal Nuclei
Masses of gray matter that lie within each hemisphere deep to the floor of the lateral ventricle
They are embedded into the white matter of the cerebrum
Functions of Basal Nuclei
Involved with the subconscious control of skeletal muscle tone and the coordination of learned movement patterns
White Matter of the Cerebrum
Association Fibers
Projection Fibers
Commissural Fibers
Association Fibers
Interconnect cortical areas within the same hemisphere
Projection Fibers
Connect cerebral cortex to diencephalon, brain stem, cerebellum, and spinal cord
Commissural Fibers
Interconnect and permit communication between the cerebral hemispheres
Frontal Lobe
Primary motor cortex - voluntary control of skeletal muscles
Temporal Lobe
Auditory cortex and olfactory cortex - conscious perception of auditory and olfactory stimuli
Parietal Lobe
Primary sensory cortex - conscious perception of touch, pressure, pain, vibration, taste, and temperature
Occipital Lobe
Visual cortex - conscious perception of visual stimuli
Primary Motor Cortex
Neurons of the primry motor cortex direct voluntary movements by controlling somatic motor neurons in the brain stem and spinal cord
Acts like a keyboard of a piano - if you stimulate a specific motor neuron, you generate a contraction in a specific skeletal muscle
Premotor Cortex
Coordiates learned movements
When you perform a voluntary movement, the premotor cortex relays the instructions to the primary motor cortex
Integrative Centers
Areas that receive information from many association areas and direct extremely complex motor activities
The General Interpretive Area
Wernicke’s area; Present in only one hemisphere, typically the left
This analytical center receives information from all the sensory association areas
Plays an essential role in your personality by integrating sensory information and coordinating access to complex visual and auditory memories
The Speech Center
Broca’s area
This center lies along the edge of the premotor cortex in the same hemisphere as the general interpretive area (usually the left).
The speech center regulate the patters of breathing and vocalization needed for normal speeech
Prefrontal Cortex
Coordinates information relayed from the association areas of the entire cortex
Cranial Nerves
- Olfactory (S)
- Optic (S)
- Oculomotor (M)
- Trochlear (M)
- Trigeminal (B)
- Abducens (M)
- Facial (B)
- Vestibulocochlear (S)
- Glossopharyngeal (B)
- Vagus (B)
- Spinal Accessory (M)
- Hypoglossal (M)
Cranial Nerves Mnemonic
O O O To Touch And Feel Very Good Velvet Such Heaven
Cranial Nerves - Sensory, Motor, or Both Mnemonic
Some Say Marry Money But My Brother Says Big Brains Matter More
Olfactory Nerve
Cranial Nerve 1 - Sensory
Sense of smell
Optic Nerve
Cranial Nerve 2 - Sensory
Sense of sight
Oculomotor
Cranial Nerve 3 - Motor
Eyelid and eyeball movement
Trochlear
Cranial Nerve 4 - Motor
Looking down at nose
Trigeminal
Cranial Nerve 5 - Both
Chewing, face, mouth, touch, and pain
Abducens
Cranial Nerve 6 - Motor
Turn eyes laterally
Facial
Cranial Nerve 7 - Both
Most facial expressions, secretion of tears and saliva
Vestibulocochlear
Cranial Nerve 8 - Sensory
Hearing and equilibrium
Glossopharyngeal
Cranial Nerve 9 - Both
Taste and blood pressure
Vagus
Cranial Nerve 10 - Both
Heart rate, digestive organs, test, aortic blood pressure
Spinal Accessory
Cranial Nerve 11 - Motor
Controls trapezius and sternocleidomastoid, swallowing
Hypoglossal
Cranial Nerve 12 - Motor
Controls tongue movement
Receptor
Passes information to the CNS in the form of action potentials along the axon of a sensory neuron
Functions of Receptors
- Adequate stimulus - each receptor has a characteristic sensitivity that detects stimulus
- Transduction - conversion of a sensory stimulus from one form to another
- Interpretation
Types of Receptors
Nocioceptors, thermoreceptors, and mechanoreceptors
Nocioceptors
Pain receptors; especially common in the superficial portions of the skin, in join capsules, within the periostea of bones and around the walls of blood vessels
May be sensitive to:
- Extreme temperatures
- Mechanical damage
- Dissolved chemicals
Thermoreceptors
Temperature receptors; free nerve endings located in the dermis, in skeletal muscles, in the liver, and in the hypothalamus
Cold receptors are 3-4x more numerous than warm receptor
Mechanoreceptors
Sensitive to stimuli that distort their plasma membranes; these membranes contain mechincally gated ion channels
Three Classes:
- Tactile receptors
- Baroreceptors
- Proprioceptors
Tactile Receptors
Provide the closely related sensations of touch, pressure, and vibration.
Touch sensations provide information about shape or texture.
Baroreceptors
Detect pressure changes in the walls of blood vessels and in portions of the digestive, respiratory, and urinary tracts
Proprioceptors
Monitor the positions of joins and skeletal muscles
They are the most structurally and functionally complex of the general sensory receptors.
Chemoreceptors
Specialized nerve cells that can detect small changes in the concentration of specific chemicals or compounds
Somatic Sensory Pathways
Carry sensory information from the skin and muscles of the body wall, head, neck and limbs.
3 Major Pathways:
- Spinothalamic pathway
- Posterior column pathway
- Spinocerebellar pathway
Spinothalamic Pathway
Carries sensations of poorly localized touch, pressure, pain, and temperature
This pathways includes small tracts that deliver sensations to reflex centers in the brain stem as well as larger tracts that carry sensations destined for the cerebral cortex
Example: phantom limb pain
Anterior Spinothalamic Tract
Carry crude touch and pressure sensations
Lateral Spinothalamic Tract
Carry pain and temperature sensations
Posterior Columns
Carries sensations of highly localized (“fine”) touch, pressure, vibration, and proprioception
Starts at the peripheral receptor and ends at the primary sensory cortex of the cerebral hemisphere
Posterior Spinocerebellar Tracts
Contain axons that do not cross over to the opposite side of the spinal cord
These axons reach the cerebellar cortex by the inferior cerebellar peduncle of that side
Anterior Spinocerebellar Tracts
Dominated by axons that have crossed over to the opposite side of the spinal cord
Visceral Pathways
Visceral sensory information is collected by interoceptors monitoring visceral tissues and organs primarily within the thoracic and abdominopelvic cavities
Cranial nerves 5, 7, 9, and 10 carry information along these pathways from the mouth, palate, pharynx, larynx, trachea esophagus, and associated vessels and glands.
Solitary Nucleus
Large nucleus on each side of the medulla oblongata
Major processing and sorting center for visceral sensory information
Corticospinal Pathway
AKA Pyramidal System
Provides voluntary control over skeletal muscles
Direct - the upper motor neurons synapse directly on the lower motor neurons
Can also be indirectly as it innervates centers of the medial and lateral pathways
3 Pairs of Descending Tracts in the Corticospinal Pathway
- Corticobulbar tract
- Lateral corticospinal tracts
- Anterior cortiocspinal tract
These tracts enter the white matter of the internal capsule, descend into the brain stem, and emerge on either side of the midrain as the cerebral peduncles
Corticobulbar Tract
Axons synapse on lower motor neurons in the motor nuclei of cranial nerves 3-7, 9, 11, and 12
Provides conscious control over skeletal muscles that move the eye, jaw, and face, and some muscles of the neck and pharynx
Innervate the motor centers of the medial and lateral pathways
Lateral Corticospinal Tracts
Cross the spinal cord; run on the opposite side of the spinal cord
Anterior Corticospinal Tracts
Uncrossed along the spinal cord
Extrapyramidal
Medial and Lateral pathways
The components of the medial pathways help control gross movements of the trunk and proximal limb muslces, and those of the lateral pathway help control the distal limb muscles that perform more precise movements
Medial Pathways
Primarily concerned with the control of muscle tone and gross movements of the neck trunk and proximal limb muscles.
Vestibulospinal Tracts
Descending tracts of the medial pathway that carry involuntary motor commands issued by the vestibular nucleus to stabilize the position of the head.
Tectospinal Tract
Descending tracts of the medial pathway that carry involuntary motor commands issued by the colliculi
Reticulospinal Tract
Descending tracts of the medial pathway that carry involuntary motor commands issued by neurons of the reticular formation
Lateral Pathways
Primarily concerned with the control of muscle tone and the more precise movements of the distal parts of the limb
Rubrospinal Tracts
Descending tracts of the lateral pathway that carry involuntary motor commands issued by the red nucleus of the mesencephalon
Basal Nuclei
Responsible for coordination and feedback control over muscle contraction
Provide the background patters of movement involved in voluntary motor activities
Two Major Pathways for Basal Nuclei
- One group of axons synapses on thalamic neurons, whose axons extend to the premotor cortex, the motor association area that directs activities of the primary motor cortex. This arrangement creates a feedback loop that changes the sensitivity of the pyramidal cells and alters the pattern of instructions carried by the corticospinal tracts.
- A second group of axons synapses in the reticular formation, altering the excitatory or inhibitory output of the reticulospinal tracts.
Two Populations of Interneurons in Basal Nuclei
One that stimulates neurons by releasing acetylcholine (ACh) and another that inhibits neurons by releasing gamma aminobutyric acid (GABA)
Role of the Cerebellum
Monitors proprioceptive (position) sensations, visual information from the eyes, and vestibular (balance) sensation from the interal ear as movements are under way.
The patterns of cerebellar activity are learned by trial and error, over many repetitions. Many of the basic patterns are established early in life.
All motor pathways send information to the cerebellum when motor commands are issued. As the movement proceeds, the cerebellum monitors proprioceptive and vestibular information, comparing the arriving sensations with those experienced during previous movements. It then adjusts the activities of the upper motor neurons involved.
Autonomic Nervous System
Involved in the unconscious regulation of visceral functions and has sympathetic and parasympathetic divisions
Coordinates cardiovascular, respiratory, digestive, urinary and reproductive functions
Preganglionic Neuron
Visceral motor neurons in the brain stem and spinal cord that extend to ganglia
Part of visceral reflex arcs - most of their activities represent direct reflex response rather than responses to commands from the hypothalamus
Postganglionic Neuron
Preganglionic fibers leave the CNS and synapse on postganglionic neurons which are visceral motor neurons in peripheral ganglia
Innervate visceral effectors such as smooth muscle, glands, cardiac muscle, and adipocytes
Autonomic Ganglion
A collection of visceral motor neurons (postsganglionic neurons) outside the central nervous system
Preganglionic Fibers
Axons of preganglionic neurons
Postganglionic Fibers
Axons of postganglionic neurons
Divisions of the ANS
Sympathetic, Parasympathetic and Enteric
Sympathetic Nervous System
“Kicks in” only during exertion, stress, or emergency
“Fight or flight” response
Readies the body for a crisis that may require sudden, intense physical activity
Parasympathetic Nervous System
“Rest and Digest” response
Conserves energy and promotes sedentary activities, such as digestion
Stimulates visceral activity; body relaxes, energy demands are minimal, and both your heart rate and blood pressure are relatively low while your digestive organs are highly stimulated
Enteric Nervous System
An extensive network of neurons and nerve networks in the walls of the digestive tract
Paravertebral (Sympathetic Chain) Ganglia
Lie on both sides of the vertebral column
Neurons in these ganglia control effectors in the body wall, inside the thoracic cavity, and in the head and limbs
Prevertebral (Collateral) Ganglia
Anterior to the vertebral bodies
Contain ganglionic neurons that innervate tissues and organs in the abdominopelivic cavity
Adrenal Medulla
Center of each adrenal gland
It is a modified sympathetic ganglion; the ganglionic neurons of the adrenal medullae have very short axons. When stimulated, they release neurotransmitters into the bloodstream, not at a synapse.
Ventricle
One of four fluid filled interior chambers of the brain
Commisural
Crosses over from side to the other
Proprioception
The awareness of the position of bones, joints, and muscles
Threshold
The membrane potential at which an action potential begin
Ipsilateral
A reflex response that affects the same side as the stimulus
Corneal Reflex
(S) Blinking of eyelids
Tympanic Reflex
(S) Reduced movement of the auditory ossicles
Auditory Reflex
(S) Eye and/or head movements triggered by sudden sounds
Vestibulo-ocular Reflex
(S) Opposite movement of eyes to stabilize field of vision
Direct Light Reflex
(V) Constriction of ipsilateral pupil
Consensual Light Reflex
(V) Constriction of contralateral pupil
