Chapters 4-6 Flashcards
What are neurons?
There are approximately 100 billion neurons in the human brain, and each individual neuron is part of the vast interconnected communications network that forms the human nervous system. Each neuron is analogous to a single computer that is connected to the millions or billions of other computers on the Internet.
Structure of neurons include?
Cell body Dendrites Axon (nerve fibre) Action potential Myelinated neruons Unmyelinated neurons Synapse Neurontransmitters
What are Cell body?
contains various organelles (for e.g., mitochondria) as well as the cell nucleus.
What are Dendrites?
branches (extensions) of the cell body that receive stimulation from other neurons.
What are Axon (nerve fibre)?
carries information (action potentials) away from the cell body of the neuron.
What are Action potential?
the “all or none” electrical impulse that travels through a neuron or skeletal muscle cell.
What are Myelinated neruons?
are neurons in which the axon of the neuron is covered with a fatty, sheath-like insulating substance known as myelin. Myelin increases the transmission speed of action potentials (nerve impulses) along the axon.
What are Unmyelinated neurons?
are neurons in which the axons are not covered by myelin. Therefore, the transmission of nerve impulses in unmyelinated fibres is lower.
What are Synapse?
refers to the place of close contact between neurons
The synapse is where information is transmitted from one neuron to another, and is often used to refer to the connections between neurons (for e.g., the term monosynaptic means one synapse or connection).
What are Neurontransmitters?
are chemical substances that are released at the presynaptic nerve terminal (or axon terminal). Neurotransmitters are chemical messengers that transform and carry the information conveyed by the action potential across the synapse to the dendrite of the receiving neuron.
Types of neurons? (3)
- Sensory (afferent) neurons
- Motor (efferent)
- Interneurons
What are sensory (afferent) neurons?
these nerve cells send neural impulses (action potentials) from a sensory receptor (such as a pain receptor or touch receptor in your skin) towards the CNS.
What are motor (efferent) neurons?
these nerve cells send neural impulses (e.g., motor commands from the brain) away from the CNS and toward the skeletal muscle fibres.
What are interneurons?
these specialized nerve cells originate and terminate in the brain or spinal cord. One of their important functions is to provide a link between sensory neurons and motor neurons in the spinal cord. These connections in the spinal cord are known as reflexes and are important for the spinal control of movement.
What is the spinal cord?
- Once the impulse reaches the spinal cord, it enters through a structure known as the dorsal root (there are right and left dorsal roots), which is located at the back (or dorsal) part of the cord.
- The spinal cord is composed of two sections known as gray matter and white matter
- From the dorsal root, the action potentials travel through the dorsal horn of the gray matter and up the spinal cord in specialized tracts (a network of nerves) located in the white matter known as the dorsal (or posterior) columns.
o Because these tracts carry incoming information from the peripheral nervous system up the spinal cord to the brain, they are known as ascending tracts.
o somatosensory cortex and other specialized areas of the brain
• The tracts which are responsible for transmitting motor information down the spinal cord (i.e., from the brain to skeletal muscle fibres) are
known are descending tracts.
o These tracts form the sensory and motor pathways through which the central nervous system controls movement.
What is the anterolateral system?
These sensory tracts are located at the front (anterior) and sides (lateral) of the spinal cord (as opposed to the back of the cord in the case of the dorsal columns).
• These tracts transmit sensory information to different parts of the brain such as the thalamus and cerebellum.
What is the Anterior spinocerebellar tract?
Connects the spinal cord to the cerebellum and is located on the anterior aspect of the cord.
What is the Lateral spinothalamic tract?
Connects the spinal cord to the thalamus and is located on the lateral aspect of the cord.
The typical route taken by neural impulses as they travel up the dorsal column and spinocerebellar tracts respectively, and through different parts of the brain on their way to the somatosensory (or sensory) cortex, which is an important part of the brain for processing sensory information.
Explain the Dorsal Column Pathway?
Dorsal column → Brainstem → Hypothalamus → Thalamus → Somatosensory cortex
Explain the Spinocerebellar Pathway?
Spinocerebellar tract → Brainstem → Cerebellum → Somatosensory cortex
The primary descending (motor) tract is the pyramidal (or corticospinal ) tract which is located what part of cord?
on the lateral aspect of the spinal cord.
As with the sensory pathways, there are additional motor pathways that transmit information away from the brain. Explain them.
- Collectively, these pathways are known as the extrapyramidal tracts (or system) and can be found on the anterior aspect of the cord.
- Some examples of these secondary pathways are the rubrospinal tract and the vestibulospinal tract .
- Once the motor commands reach the appropriate spinal level, they exit at the front of the cord through a structure known as the ventral root.
What is a Volitational Act?
- is usually intended to achieve a specific objective (i.e., movements are goal-directed)
What is Synaptic Proliferation?
after a few months dramatic changes in the control of movement begin to occur as the brain continues to develop and form new connections
What is Typical Motor Pathway?
Cortical Motor Neuron → Upper Motor Neuron → Interneuron → Lower Motor Neuron
What is Gray matter?
is a gray coloured, butterfly-shaped looking central portion of the spinal cord. It contains the cell bodies of interneurons that lie in the centre of the cord.
What is White matter?
is the white-coloured, peripheral part of the spinal cord that surrounds the gray matter. It contains the myelinated axons of sensory and motor neurons, which give it its white appearance.
What is Dorsal root?
is the structure through which sensory information enters the spinal cord.
What is Ventral root?
is the structure through which motor information exits the spinal cord.
What are Dorsal (posterior) columns? (What does it do in terms of sensory information?)
transmits information about proprioception, touch, and pressure to the somatosensory cortex and other parts of the brain.
What sensations does Anterolateral system deal with? What tracts does it have?
contains the spinocerebellar and spinothalamic tracts which transmit pain, temperature, pressure, and touch information to the thalamus and cerebellum.
What is the Pyramidal tract system?
is the primary motor pathway through which neural impulses reach skeletal muscles from the brain.
What are Extrapyramidal tracts?
are secondary pathways carrying efferent information.
What sections are the brain organized into?
- the brainstem,
- the cerebellum
- the cerebrum.
What is the brainstem?
- in evolutionary terms, the brainstem is the older, more “primitive” part of the brain, which is located at the top of the spinal cord. It is responsible for regulating basic “life-support” physiological processes such as breathing, heart rate, blood pressure and digestion
What is the cerebellum?
is located at the base of the cerebrum and just posterior to the brainstem. The cerebellum is frequently called the “little brain” and is an important centre for balance control and movement. One of its functions is to process (i.e., match and compare) the outgoing motor commands with the incoming sensory feedback that occurred as the result of the movement.
What is the cerebrum?
is the primary brain structure that consists of the right and left cerebral hemispheres. The cerebrum is covered with a highly dense layer of neurons known as the cerebral cortex.
What are the main areas in the brainstem involved in motor control?
a. reticular formation
b. pons
c. medulla oblongata (see below for further information).
d. The brainstem is also an important centre for the monitoring and regulation of reflexes.
What is the cerebral cortex?
the cortex covers the right and left cerebral hemispheres with an undulating, wrinkly, gray surface. The cortex is where the higher brain functions such as cognition (thinking, intelligence, decision-making, planning) and information processing (e.g., sensory perception) occur.
What is the Reticular Formation?
Provides an important link between sensory input and motor output, in that its primary function is as an integrator of sensory and motor information (for e.g., it can regulate motor output based on the sensory input it receives).
What is the Pons?
The pons is involved in the control of automatic movements such as breathing, chewing and swallowing, and may also play a role in the control of balance.
What is the Medulla oblongata?
Acts as a regulatory agent for internal physiological processes such as the control of heart rate and respiration. Most significantly, it is also the point at which sensory and motor tracts cross over to the other side of the body (i.e., the sensory and motor fibres from the left side of the body cross over to the right side at the level of the medulla oblongata, to be controlled by the right side of the brain, and vice versa). This crossing over is called a decussation.
What is the Hypothalamus?
• Some of its primary functions are to control the endocrine system (hormones) and to regulate body homeostasis (for example, it regulates body temperature, hunger, thirst and the physiological response to stress).
What is the Thalamus?
Is an important relay station for sensory input on its way to the higher brain centres. It functions very much like the central post office of a city, which receives all the mail for that city, and then sorts it and sends it to the appropriate local post office so it can reach its destination. The thalamus also play an important role in the control of attention
What is the Frontal Lobe?
Contains the motor cortex, which is the primary centre for the production of movement. The frontal lobe is involved with planning, coordinating and executing behaviour.
What is the Parietal lobe?
Interacts with the motor cortex and the supplementary motor area (SMA). It contains the somatosensory cortex which is the primary centre for receiving and processing sensory information.
What is the Occipital lobe?
Is an important centre for processing visual input.
What is the Temporal lobe?
Is an important centre for memory and language.
What is the Somatosensory cortex?
It forms part of the cerebral cortex and is located posterior to the central sulcus, which separates the parietal lobe from the frontal lobe. It includes several specific regions that receive sensory information transmitted via the sensory nerves that are specific to that type of information (for example, proprioception).
Collectively, the hypothalamus and thalamus form what is known as?
The diencephalon
The motor areas are?
- Primary motor cortex
- Premotor area
- Supplementary motor area (SMA)
What is the Primary motor cortex?
Is the primary motor centre responsible for the production of movement. It sends neural impulses (motor commands) down the pyramidal system (corticospinal tracts) to the α -motor neurons that travel to the skeletal muscle fibres.
What is the Premotor area?
Is involved in planning and movement preparation and plays an important role in rhythmic coordination.
What is the Supplementary motor area (SMA)?
Is also involved in movement planning, particularly in relation to the planning and preparation of sequential movements.
What does redundancy mean?
that if one centre is incapacitated and can no longer function, there is enough overlap that other centres may be able to compensate
Two other important centres of the brain that are responsible for controlling movement are?
1) the cerebellum
2) the basal ganglia.
What does the cerebellum do?
the cerebellum plays an important role in the production of coordinated movement and the control of balance. In general, it functions as an error detection and correction system which assists in the production of smooth, coordinated movements.
o It is believed that a copy of the motor commands (called an efference copy) is sent by the motor cortex to the cerebellum, so that the cerebellum can “predict” the sensory feedback that will be generated as a result of performing the movements.
o When the “real” sensory feedback reaches the cerebellum (via the spinocerebellar tract), it is thought that the cerebellum compares the actual sensory feedback to the predicted sensory feedback.
o If the outcome (real feedback) is inconsistent with the intended movement (predicted feedback), then the cerebellum provides error correction information to the motor cortex (to make the necessary adjustments) so that the movement will become more efficient and coordinated.
What does the basal ganglia do?
this structure is made up of 4 large clusters of neurons. Collectively, the basal ganglia are involved in movement initiation, control of muscle force and muscle antagonist activity. The basal ganglia are most commonly associated with the disease known as Parkinson’s disease. Parkinson’s disease is a neuromotor disorder which is caused by a lack of dopamine (a neurotransmitter) in the basal ganglia. It is characterized by tremors, rigidity and very slow movements (bradykinesia).
