Physiology of the Nervous System: Central Nervous System

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Questions and Answers

What percentage of corticospinal tract originates from the primary motor cortex?

30%

What is the function of the corticospinal tract?

Transmission of motor signals from the motor cortex to the muscles

What is the location of the pyramids in the corticospinal tract?

In the medulla

What is the function of the brain stem?

Control of various motor and sensory functions, including respiration, cardiovascular system, gastrointestinal function, stereotyped movements, and equilibrium Signup and view all the answers

What percentage of corticospinal tract fibers cross to the opposite side of the cord?

Majority (most) Signup and view all the answers

What is the function of the basal ganglia, cerebellum, and various nuclei of the brain stem?

Indirect transmission of motor signals from the motor cortex to the muscles Signup and view all the answers

Where do the corticospinal tracts terminate?

Principally on the interneurons of the cord gray matter Signup and view all the answers

How many neurons are estimated to be present in the central nervous system?

80 to 100 billion neurons Signup and view all the answers

What is the name of the pathway that transmits motor signals from the motor cortex to the muscles?

Corticospinal tract (pyramidal tract) Signup and view all the answers

Where are the synapses located on a typical brain neuron?

mostly on the neuronal dendrites, but also on the cell body Signup and view all the answers

What is the normal direction of signal transmission in a neuron?

from the axon of a preceding neuron to dendrites of subsequent neurons Signup and view all the answers

What is the primary function of sensory receptors in the nervous system?

to initiate activities of the nervous system Signup and view all the answers

What are the different types of responses to sensory stimuli?

Immediate reaction from the brain and stored responses (as memory) for future dates Signup and view all the answers

What part of the brain controls subconscious activities of the body?

Lower brain or subcortical level (medulla, pons, mid-brain, thalamus, hypothalamus, cerebellum, and basal ganglia) Signup and view all the answers

What is the function of the cerebellum in controlling equilibrium?

Combined function with the reticular substance of brainstem Signup and view all the answers

What are the five regions of the central nervous system where sensory information is conducted?

the spinal cord, reticular substance, cerebellum, thalamus, and areas of the cerebral cortex Signup and view all the answers

What are emotional patterns controlled by?

Areas in the medulla, pons, mesencephalon, amygdala, and hypothalamus Signup and view all the answers

What is the primary role of the motor part of the CNS?

to control various bodily activities through effector organs Signup and view all the answers

What is the term for the pathway through which sensory information is transmitted from the peripheral nerves to the CNS?

somatosensory axis Signup and view all the answers

What is the function of the cerebral cortex?

Extremely large memory storehouse and 'seat of intelligence' Signup and view all the answers

What initiates wakefulness in the cerebral cortex?

Lower brain centers Signup and view all the answers

What are the three major parts of a neuron?

Soma, axon, and dendrites Signup and view all the answers

What is the function of presynaptic terminals in a synapse?

To secrete excitatory or inhibitory neurotransmitters Signup and view all the answers

What is a chemical synapse?

A type of synapse where the presynaptic terminal of one neuron releases neurotransmitters that bind to receptors on the postsynaptic neuron Signup and view all the answers

Where do visual signals terminate in the brain?

occipital lobe Signup and view all the answers

What is the primary function of the motor cortex?

control motor activity Signup and view all the answers

Which part of the brain is concerned with controlling the muscles of the hands and the muscles of speech?

primary motor cortex Signup and view all the answers

What is the function of the premotor area?

generate complex patterns of movement Signup and view all the answers

What is the supplementary motor area responsible for?

attitudinal and fixation movements Signup and view all the answers

Where is the primary motor cortex located?

first convolution of the frontal lobes anterior to the central sulcus Signup and view all the answers

What is the role of nerve signals from multiple cortical and non-cortical brain regions in the motor cortex?

control motor functions Signup and view all the answers

What is the relationship between the supplementary motor area and the premotor area?

they function together Signup and view all the answers

What type of sensations are transmitted through the dorsal column-medial lemniscal system?

Touch sensations requiring a high degree of localization, vibration, and sensations that signal movement against the skin Signup and view all the answers

What is the function of the anterolateral pathway?

Transmits rapidly changing or repetitive signals, including pain, thermal sensations, and crude touch and pressure sensations Signup and view all the answers

What is the role of the somatosensory cortex?

To receive and interpret somatosensory signals Signup and view all the answers

What is the significance of Brodman's areas in the somatosensory cortex?

They are based on histological differences Signup and view all the answers

Where do sensory signals from all modalities of sensation terminate?

In the cerebral cortex immediately posterior to the central fissure Signup and view all the answers

What is the function of the brain stem in the transmission of somatosensory signals?

Signals are transmitted to the thalamic nuclei and then to the somatosensory cortex Signup and view all the answers

What is the significance of the central fissure (central sulcus) in the somatosensory cortex?

It extends horizontally across the brain and separates the region for sensory reception and interpretation from other brain regions Signup and view all the answers

What is the significance of the anterior half of the parietal lobe?

It is concerned almost entirely with reception and interpretation of somatosensory signals Signup and view all the answers

Study Notes

General Design of the Nervous System

The central nervous system is estimated to contain 80 to 100 billion neurons.
A typical brain neuron receives incoming signals through synapses located mostly on dendrites, but also on the cell body.
A neuron can have only a few hundred or as many as 200,000 synaptic connections from input fibers.
The output signal travels by way of a single axon leaving the neuron, which may have many separate branches to other parts of the nervous system or peripheral body.

Sensory Part of CNS: Sensory Receptors

Most activities of the nervous system are initiated by exciting sensory receptors, such as:
- Visual receptors in the eyes
- Auditory receptors in the ears
- Tactile receptors on the surface of the body
Sensory information enters the central nervous system through peripheral nerves and is conducted to multiple sensory areas, including:
- Spinal cord at all levels
- Reticular substance of the medulla, pons, and mesencephalon of the brain
- Cerebellum
- Thalamus
- Areas of the cerebral cortex

Motor Part of CNS – Effector Organ

The most important eventual role of the nervous system is to control various bodily activities.
The motor part of the CNS is divided into two levels:
- Lower brain or subcortical level: controls subconscious activities of the body, such as:
  - Control of arterial pressure and respiration
  - Control of equilibrium
  - Feeding reflexes
  - Emotional patterns
- Higher brain or cortical level: responsible for higher functions, such as:
  - Reading, writing, and speaking
  - Calculations and composing music
  - Memory storage and retrieval

The Synapse

A neuron is composed of three major parts: the soma, axon, and dendrites.
The presynaptic terminals of the first neuron synapse with the dendrite or soma of the second neuron.
Synapses can be either excitatory (secreting excitatory neurotransmitter) or inhibitory (secreting inhibitory neurotransmitter), depending on the type of postsynaptic receptor.

Transmission of Signals from the Motor Cortex to the Muscles

Motor signals are transmitted from the cortex:
- Directly to the spinal cord through the corticospinal tract (pyramidal tract)
- Indirectly through multiple accessory pathways that involve the basal ganglia, cerebellum, and various nuclei of the brain stem (extrapyramidal system)
The corticospinal tract originates from the primary motor cortex, premotor and supplementary motor cortex, and somatosensory cortex.

Brain Stem Control of Motor Functions

The brain stem consists of the medulla, pons, and midbrain (mesencephalon).
The brain stem contains motor and sensory nuclei that perform motor and sensory functions for the face and head regions.
The brain stem is also involved in controlling respiration, the cardiovascular system, and many stereotyped movements of the body.

Somatosensory Cortex

The somatosensory cortex is responsible for receiving and interpreting sensory information from the body.
The somatosensory cortex is divided into two areas: somatosensory area I and somatosensory area II.
The central fissure (central sulcus) separates the two areas, with the anterior half of the parietal lobe concerned with reception and interpretation of somatosensory signals.

Motor Pathways and Autonomic Nervous System

The motor cortex controls motor activity and is divided into three subareas: primary motor cortex, premotor area, and supplementary motor area.
The primary motor cortex controls discrete movements, while the premotor area and supplementary motor area control more complex movements and attitudinal movements of the body.

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Description

This quiz covers the basics of the central nervous system, including the structure and function of neurons and synapses.