Human nervous system

What are two main components of the central nervous system?

• The Brain – the control center for processing sensory information, initiating motor activity, and managing higher functions like thought, memory, and emotion.

• The Spinal Cord – the communication highway between the brain and the rest of the body; it transmits nerve signals and coordinates reflexes.

Name the four lobes of the cerebreal cortex. What is a primary function associated with each lobe?

1. Frontal Lobe

• Responsible for executive functions such as reasoning, planning, decision-making, problem-solving, and emotional regulation.

• Also involved in voluntary motor control.

2. Parietal Lobe

• Processes sensory information from the body, including touch, temperature, pain, and pressure.

• Helps with spatial awareness and navigation.

3. Temporal Lobe

• Involved in processing auditory information, recognizing language, and forming and retrieving memories.

4. Occipital Lobe

• The brain’s visual processing center — it interprets information received from the eyes.

What are the three main parts of the brainstem, listed from superior to inferior?

1. Midbrain – involved in visual and auditory reflexes, and coordinating movement.

2. Pons – helps regulate breathing, sleep, and relays signals between the cerebrum and cerebellum.

3. Medulla Oblongata – controls vital autonomic functions such as heart rate, blood pressure, and respiration.

Describe the role of the thalamus in sensory processing. What other brain region is it closely associated with functionally?

The thalamus acts as the brain’s central relay station for sensory information. Nearly all sensory signals (except smell) pass through the thalamus on their way to the cerebral cortex, where they are interpreted consciously.

• It receives input from the eyes, ears, skin, and other sensory organs.

• Then it filters and directs this information to the appropriate area of the cortex for processing — e.g., visual data to the occipital lobe, sound to the temporal lobe.

The thalamus is functionally closely associated with the cerebral cortex, especially because:

• It coordinates and refines incoming sensory data before it reaches conscious awareness.

• It also participates in feedback loops with the cortex for regulating attention, alertness, and even some aspects of motor control.

What is the primary function of the cerebellum? Explain why damage to the cerebellum might result in difficulty with fine motor movements.

The primary function of the cerebellum is to coordinate voluntary movements and ensure they are smooth, balanced, and precise. It also plays a key role in:

• Maintaining posture and balance

• Controlling muscle tone

• Fine-tuning motor activity based on feedback from the body and cerebral cortex

• Motor learning, like learning to ride a bike or play an instrument

When the cerebellum is damaged, a person may struggle with fine motor movements because:

• The cerebellum can no longer accurately process input from muscles, joints, and the cortex.

• Movements become uncoordinated (a condition called ataxia).

• Tasks requiring precision, like buttoning a shirt, writing, or speaking clearly, become difficult.

• The person may also show signs of tremors, imbalance, or a wide, staggering gait.

What is the corpus callosum and what is its main function?

The corpus callosum is a thick band of nerve fibers that connects the left and right cerebral hemispheres of the brain.

Main Function: Its primary role is to enable communication between the two hemispheres.

This allows:

• Integration of sensory, motor, and cognitive information from both sides of the body

• Coordination of complex tasks that require input from both hemispheres (e.g., language processing, spatial reasoning, motor control)

Explain the concept of decussation in the central nervous system. Provide one example of a pathway that exhibits decussation.

+Decussation refers to the process by which nerve fibers cross from one side of the central nervous system (CNS) to the other. This crossing often occurs in the brainstem or spinal cord, and it means that each side of the brain controls or senses the opposite (contralateral) side of the body.

+Because of decussation, damage to one side of the brain often affects the opposite side of the body. For example, a stroke in the left hemisphere may cause weakness or paralysis on the right side.

Example: Corticospinal (Motor) Tract

• This descending motor pathway carries voluntary movement commands from the cerebral cortex to the spinal cord.

• Most of its fibers decussate in the medulla oblongata (called the pyramidal decussation).

• As a result, the left motor cortex controls right-side muscles, and the right motor cortex controls left-side muscles.

What are spinal nerves and where do they originate? What types of signals do they carry?

Spinal nerves are mixed nerves that connect the spinal cord to the rest of the body, allowing communication between the brain and the periphery (limbs, organs, skin, etc.)

• Spinal nerves originate from the spinal cord.

• They emerge in pairs — one from each side of every spinal segment.

• There are 31 pairs of spinal nerves in total, divided into cervical, thoracic, lumbar, sacral, and coccygeal levels.

Each spinal nerve forms from the fusion of two roots:

• A dorsal (posterior) root, which carries sensory information into the spinal cord

• A ventral (anterior) root, which carries motor commands out to the muscles

Signals they carry:

• Sensory (afferent) signals: Information from the body (e.g. touch, pain, temperature) to the spinal cord and brain

• Motor (efferent) signals: Commands from the spinal cord/brain to muscles and glands

What is the autonomic nervous system? Briefly describe the two main divisions of the ANS and their general functions.

The autonomic nervous system (ANS) is a division of the peripheral nervous system that regulates involuntary bodily functions — the ones that happen automatically, without conscious effort. It controls activities such as heart rate, digestion, respiratory rate, pupil size, urination, and blood pressure.

Two Main Divisions of the ANS:

1. Sympathetic Nervous System – “Fight or Flight”

• Activates the body during stress or emergency situations

• Increases heart rate, dilates pupils, opens airways, and redirects blood to muscles

• Slows down digestion and urinary activity

• Prepares the body for action

2. Parasympathetic Nervous System – “Rest and Digest”

• Promotes relaxation and conserves energy

• Slows heart rate, stimulates digestion, and encourages waste elimination

• Constricts pupils and promotes calm bodily functions

• Helps maintain long-term health and balance

Explain the importance of understanding the anatomy of the brain and its pathways in diagnosing neurological damage

Why It Matters:

• Different brain regions control specific functions.

For example:

• The occipital lobe handles vision

• The frontal lobe controls decision-making and voluntary movement

• The left motor cortex governs movement on the right side of the body

• Pathways are highly organized.

Sensory and motor tracts follow predictable routes (e.g., the corticospinal tract for motor control), and they often cross over (decussate), meaning symptoms on one side of the body may trace back to damage on the opposite side of the brain.

• Helps differentiate central vs. peripheral problems.

For instance, numbness caused by spinal nerve damage is different from numbness caused by a stroke.

• Essential for imaging interpretation.

Understanding the brain’s layout helps doctors read MRIs, CT scans, and recognize abnormalities like tumors, bleeds, or infarcts.

What is a neuron and what are its main parts?

A neuron is the basic working unit of the nervous system, designed to transmit electrical signals. It consists of a cell body (soma), dendrites that receive incoming signals, and a long axon that sends signals to other neurons or muscles.

+Neurons communicate at junctions called synapses

What role does myelin play in nerve conduction?

+Myelin is a fatty insulating layer that wraps around axons and greatly increases the speed of electrical signal transmission

+It allows the action potential to jump between gaps in the myelin (nodes of Ranvier) in a process called saltotory conduction.

How does a neuron communicate with another neuron?

+When an action potential reaches the end of an axon, it triggers the release of neurotransmitters into the synapse.

+These chemicals bind to receptors on the next neuron, causing ion channels to open and potentially triggering new action potential.

What is difference between excitatory and inhibitory neurotransmitters?

+Excitatory neurotransmitter, like glutamate, increase the likehood that the receiving neuron will fire by depolarizing its membrane.

+Inhibitory neurotransmittersm like GABA, make it less likely to fire by hyperpolarizing the membrane.

How does the brain interpret the strength of a stimulus?

+The brain determines stimulus strength based on the frequency of action potentials (not their sizes)

+Stronger stimuli cause neurons to fire more rapidly or involve more neurons firing at once - a process managed through temporal and spatial summation

What is temporal summation?

Temporal summation occurs when one neuron sends multiple signals in a quick succession. These signals add up over time and can bring the target neuron to threshold, causing it to fire an action potential.

What is spatial summation?

+Spatial summation happens when signals from multiple neurons arrive at the same target neuron at the same time. If enough of these signals are excitatory, they can combine to reach the threshold and trigger an action potential.

Why is the resting membrane potential negative, and what force is responsible for maintaining it?

The resting membrane potential is negative (typically –65 to –70 mV) because there are more positive ions (mainly K⁺) leaving the cell than entering it. This is due to leaky K⁺ channels and the action of the Na⁺/K⁺ pump, which actively moves 3 Na⁺ out and 2 K⁺ in. The unequal movement of ions and their separation across the membrane creates an electrical difference that makes the inside of the cell more negative relative to the outside.

How does synaptic transmission convert an electrical signal into a chemical one, and back again?

When an action potential reaches the axon terminal, it causes voltage-gated Ca²⁺ channels to open. Calcium enters, triggering vesicles to release neurotransmitters into the synaptic cleft. These chemicals bind to receptors on the next neuron’s membrane, opening ion channels that start a new electrical signal — completing the conversion loop.