7. Nervous Control of Muscular Movement Flashcards
2 Divisions of the Nervous System
A. Central Nervous System (CNS) –
Brain and Spinal Cord
B. Peripheral Nervous System (PNS) - Afferent and Efferent divisions
3 parts of the brain
a) Forebrain
(i) Cerebrum constitutes about 80% of total brain weight
- cerebral cortex, basal nuclei
(ii) Diencephalon - thalamus, hypothalamus
b) Cerebellum
c) Brainstem - continuous with the spinal cord - medulla, pons, midbrain
Organization of the Nervous System
Afferent vs Efferent
Afferent is information going out
Efferent is information coming in
Cerebral Cortex of the Brain
Bones in the skull
What is the Spinal Cord?
transmitting sensory and motor information between the brain and the rest of the body.
- long cylinder of nerve tissue which extends down from the brainstem to the second lumbar vertebrae.
- 45 cm long and 2 cm in diameter.
- Protected by the vertebral column and associated ligaments and muscles,
- the spinal meninges
- the cerebrospinal fluid.
Meninges on Spinal Cord
Peripheral Nervous System consists of…
12 pairs of cranial nerves
31 pairs of spinal nerves
How many pairs of CRANIAL nerves do we have? Number and Name them. (name 3)
What is the Afferent Division?
- Afferent division
- conveys information from the sensors in the
periphery to the central nervous system (CNS)
What is the Efferent division?
a) Somatic nervous system -
nerve fibers innervate skeletal muscle
b) Autonomic nervous system
- nerve fibers innervate smooth and cardiac
muscle and glands
(i) sympathetic division
(ii) parasympathetic division
Sympathetic vs Parasympathetic
Sympathetic and Parasympathetic effects
(white out table)
The nervous system consists of what two categories of cells?
Neuroglia and Neurons
What is Neuroglia? (4)
- comprise about 90% of the cells within the CNS.
- occupy about half of the volume of the brain.
- The four major types of glial cells serve as the connective tissue of the CNS and as such help support the neurons both physically and metabolically.
- It is estimated that there are 100 billion neurons in the brain and one trillion neuroglia.
What are Neurons?
Neuron
* Excitable
* Carry electrical signals
Examples of the Neuroglia?
What are Neurons comprised of?
- a nerve cell.
- neuron is specialized to transmit electrical signals.
- Cell body
- Axon
- Dendrites
Basic Structure of a Neuron
What are the Cell body and Axon?
- Cell body - soma - contains the nucleus
- Axon - a long fiber that conducts impulses away from the cell body.
The term “nerve fiber” is generally used in reference to an axon.
Basic Structure of a Neuron
What is a Dendrite?
A dendrite is a branch-like extension on a neuron (nerve cell) that receives incoming signals from other neurons. It acts like a receiver, gathering information and transmitting it towards the cell body, where the neuron processes these signals to determine whether to generate its own electrical impulse (action potential) for communication with other neurons.
What is the Myelin Sheath? (2)
Myelin sheath
- It is composed mainly of lipid and protein.
- insulates axons and speeds up nerve impulse transmission by allowing action potentials to jump between nodes of Ranvier
What are the Nodes of Ranvier?
Nodes of Ranvier - spaces between the segments of myelin sheath
! saltatory conduction
Why do we have Myelinated nerve fibers?
- Myelinated nerve fibers have much faster conduction velocities than unmyelinated fibers
What is Multiple Sclerosis?
Autoimmune disease – body attacks myelin sheath within CNS
* Break down in communication
* Exposed nerves can be destroyed irreversibly
* Fatigue, vision changes, numbness, loss of coordination, muscle weakness, cognitive dysfunction
What is a Synapse?
What is a Chemical Synapse?
Synapse – the region where a neuron meets its target cell
– axon to dendrite
– axon to muscle cell
Chemical synapse –
electrical signal converted to chemical signal for transmission to the postsynaptic cell
Neurons are divided into what 3 functional classes?
- Afferent neurons - carry impulses from the sensory receptors into spinal cord or brain
- Efferent neurons - transmit impulses from the CNS out to the effector organs - muscles (motor neurons) and glands
- Interneurons - lie entirely within the CNS. They account for 99% of all nerve cells.
What is Resting membrane potential?
The resting membrane potential is the electrical charge difference that exists across the cell membrane of a neuron or other excitable cells when they are not actively transmitting signals. In other words, it’s the baseline electrical state of the cell when it’s not firing an action potential.
In most neurons, the inside of the cell is negatively charged compared to the outside. This charge difference is typically around -70 millivolts (mV) in neurons. This difference in charge is maintained by the movement of ions, such as sodium (Na+), potassium (K+), and chloride (Cl-), through ion channels in the cell membrane. Sodium-potassium pumps also play a role in maintaining this potential by actively transporting sodium ions out of the cell and potassium ions into the cell.
What is an Action potential?
An action potential, also known as a nerve impulse, is a brief electrical signal that travels along the membrane of a neuron. It’s a fundamental mechanism by which neurons communicate with each other and transmit information within the nervous system.
What is the Synaptic Cleft?
Nervous information is relayed across the synaptic cleft by means of a chemical transmitter substance.
Excitatory vs Inhibitory
What is the Neuromuscular Junction?
Neuromuscular junction - nerve to muscle synapse. The chemical transmitter substance is acetylcholine.
What are Schwann Cells?
Schwann cells secrete chemical signals required for formation and maintenance of the Neuromuscular Junction
Spatial vs Temporal Summation
Spatial summation involves simultaneous signals coming from multiple presynaptic neurons being received by a single postsynaptic neuron.
Temporal summation involves a single presynaptic neuron rapid-firing signals to a postsynaptic neuron
What is ACH?
the chemical transmitter substance is acetylcholine (Ach)
What is the Spinal Cord?
- The spinal cord provide two-way conduction pathway to and from the brain, and it is a major reflex centre.
- Paired spinal nerves arise from the spinal cord
- 31 pairs of spinal nerves are attached to the spinal cord
What are the 31 pairs of spinal nerves
31 pairs of spinal nerves are attached to the spinal cord
“ 8 cervical
“ 12 thoracic
“ 5 lumbar
“ 5 sacral
“ 1 coccygeal
What are the Cervical spinal nerves?
What is cervical enlargement?
The cervical enlargement which extends from the C4 through T1 segments of the spinal cord
What is The lumbosacral enlargement?
The lumbosacral enlargement which extends from the T11 through L1 segments of the spinal cord
What is The lumbosacral enlargement?
The lumbosacral enlargement which extends from the T11 through L1 segments of the spinal cord
What is the Plexus?
Plexus – a network of converging and diverging nerve fibers, or blood vessels
differentiate between grey and white matter?
The brain and spinal cord are composed of gray matter and white matter.
- The nerve cell bodies lie in and constitute the grey matter
*axons form the white matter.
Dorsal vs Ventral Roots
Each spinal nerve has a dorsal (back) root and a ventral (front) root connected to the spinal cord.
- The dorsal roots contain afferent (sensory) fibers that carry information from the periphery to the spinal cord and brain.
- The ventral roots contain efferent (motor) fibers to the skeletal muscle.
Where are the Dorsal and Ventral Roots?
Each spinal nerve has a dorsal root and a ventral root connected to the spinal cord.
The dorsal roots contain afferent (sensory) fibers that carry information from the periphery to the spinal cord and brain.
The ventral roots contain efferent (motor) fibers to the skeletal muscle.
The cell bodies of the motor axons making up the ventral roots are located in the ventral gray horns of the spinal cord
The cell bodies of the sensory axons making up the dorsal roots are outside of the spinal cord in the spinal ganglia
What are Ganglion?
Ganglion –
a collection of nerve cell bodies located outside of the CNS.
Spinal Cord Injury
- Spinal cord injury is most often the result of trauma to the spinal cord but can also be associated with congenital or degenerative disease.
- Every year approximately 10,000 people in the USA survive an acute traumatic injury to the spinal cord.
- Causes include
– Motor vehicle accidents (36-48%)
– Violence (5-29%)
– Falls (17-21%)
– And recreational activities (7-16%)
What is quadriplegic?
The patient is quadriplegic if the cord is transected superior to C5.
” If the transection is above C4, the patient may die of respiratory failure.
What is paraplegic?
The patient is paraplegic – paralysis of both lower limbs - if the transection occurs below the cervical segment of the spinal cord.
What are Proprioceptors?
Proprioceptors
Conduct sensory information to the CNS from muscles, tendons, ligaments, and joints
What are Muscle Spindles?
Structure - several modified muscle fibers, 4 to 10 mm in length, contained in a capsule, with a sensory nerve spiralling around its center.
Muscle spindles are sensory receptors in muscles that detect changes in muscle length and contribute to our sense of body position. They help regulate muscle tone and coordinate movements by providing feedback to the nervous system.
What is the function of the Muscle Spindles?
Muscle spindles are specialized sensory receptors within muscles that detect changes in muscle length and the rate of change. They play a crucial role in reflexes, maintaining muscle tone, and providing sensory feedback for accurate motor control and body position awareness.
Remember these types
Types:
– Muscle spindles – change in length
– Golgi tendon organ – change in tension
– Joint receptors – change in angle
What are the Three ways that the muscle spindle can activate the alpha motor neurons to cause the muscle to contract?
- Tonic Stretch
- Phasic Stretch Length
- Gamma System
What is a Tonic Stretch?
Tonic stretch -
concerned with the final length of the muscle fibers
What is a Phasic Stretch Length?
Phasic stretch -
spindle responds to the velocity of the change of length
What is the Gamma System?
Gamma system - gamma efferent fibers
When the alpha motor neurons are activated, the gamma motor neurons are also activated (activation).
– Gamma system provides the mechanism for maintaining the spindle at peak operation at all muscle lengths.
– They help maintain muscle spindle sensitivity
What is a Stretch Reflex? *
Stretch reflex – e.g. patellar tendon tap
automatic response that occurs when a muscle is quickly stretched.
When a doctor taps a specific tendon, like the patellar tendon just below the knee, it stretches the quadriceps muscle. This rapid stretch triggers a reflexive contraction of the quadriceps muscle, causing the lower leg to kick forward involuntarily.
What are the Five functional components of the reflex arc? (ON EXAM)
Five functional components
* Receptor (muscle spindle)
* Afferent (sensory) neuron
* Integrating Centre (spinal cord)
* Efferent (motor) neuron (both alpha and gamma)
* Effector (muscle contraction)
What are Golgi Tendon Organs (GTO)?
In summary, Golgi tendon organs are sensory receptors that monitor muscle tension and contribute to maintaining safe levels of force during muscle contractions, helping to prevent injury and regulate muscle activity.
They are in series with the muscle fibers rather than in parallel as are muscle spindles.
- When a muscle contracts, the GTO is stretched.
What are the functions of Golgi Tendon Organs (GTO)?
Functions - the firing rate of the GTO is very sensitive to changes in the tension of the muscle.
- Sensory input from GTO about the tension produced by muscles is useful for a variety of motor acts, such as maintaining a steady gripn on an object.
- When stimulated by excessive tension or stretch -> send sensory information to the CNS -> causes the contracted muscle to relax
(reflex inhibition)
– protect the muscle and its connective tissue harness from damage due to excessive loads
What are Joint Receptors?
Supply information to the CNS concerning
* joint angle,
* acceleration of the joint
* pressure and
* pain
What are The cerebral cortex and cerebellum?
The cerebral cortex and cerebellum are the main centers
employed in learning new motor skills. These areas of the brain
initiate voluntary control of movement patterns.
More on the Cerebral Cortex and Cerebellum
The cerebral cortex (gray matter), is your brain’s outermost layer (3 to 4 mm thick) and lies on top of your cerebrum.
The cerebrum is the the largest part of the brain and is split down the middle into two cerebral hemispheres.
– The right cerebral hemisphere receives sensations from and controls movements on the left side of the body.
– The left cerebral hemisphere is concerned with sensations and movements on the right side of the body.
The cerebrum is subdivided into lobes named after the bones of the skull that lie over them.
What is the Primary motor cortex?
located at the rear of the frontal lobe of the cerebral cortex.
- Stimulation of different areas of the primary motor cortex brings about movement in different, specific areas of the body.
- Contains the motor homunculus. However, no coordinated movement can be elicited.
Motor Homunculus
What is the Corticospinal tract ?
The corticospinal tract is a neural pathway that connects the motor cortex of the brain to the spinal cord, enabling voluntary control of muscle movements. It plays a key role in executing precise and coordinated motions, essential for activities like writing and playing instruments.
What is the Premotor Cortex?
One of the three higher areas that command the primary motor cortex.
- Located on the lateral surface of each cerebral hemisphere in front of the primary motor cortex.
What is the Somatosensory Cortex?
Somatosensory Cortex
- The site for initial cortical processing of pressure, touch, heat pain and proprioceptive input
- Located in the anterior section of the parietal lobe, immediately behind the central sulcus.
- Each region within the somatosensory cortex receives sensory input from a specific area of the body.
Where is the Cerebellum?
What is the function of the Cerebellum?
The cerebellum is a part of the brain located at the back of the skull, beneath the cerebrum. Its primary function is to control and coordinate voluntary movements, balance, posture, and fine motor skills. It receives input from sensory systems, the spinal cord, and other parts of the brain to help ensure smooth and accurate movements.
Additionally, the cerebellum is involved in motor learning and procedural memory, which means it helps us acquire and refine skills over time through repetition and practice. While often associated with motor functions, the cerebellum also plays a role in certain cognitive processes, such as attention, language, and emotional regulation.
Examples of cerebellum functions?
Cerebellum
* Function - the major comparing, evaluating, and integrating center for
* postural adjustments,
– locomotion,
– maintenance of equilibrium,
– perceptions of speed of body movement,
– and general motor coordination.
What happens to an individual with a damaged cerbellum
Damage to the cerebellum results in impaired motor control. Individuals with severe
cerebellar damage cannot start or stop movements quickly or easily. They cannot easily
combine the movements of several joints into a single, smooth, coordinated motion.
Symptoms of Persons with
Cerebellar Damage (4)
- They cannot perform movements smoothly
- They walk awkwardly with their feet well apart.
- difficulty maintaining their balance
- They cannot start or stop movements quickly or easily
- They cannot easily combine the movements of several joints into a single, smooth, coordinated motion. To move the arm, they must first move the shoulder, then the elbow, and finally the wrist.
