The Brain and Methods of Study

The brain is the central processor of the nervous system, receiving sensory input and coordinating responses. Key regions include:

• Cerebral cortex: Controls higher functions like consciousness, intelligence, memory, and language
• Cerebellum: Responsible for muscle coordination
• Medulla: Regulates unconscious activities like breathing and heart rate

Vocabulary: The cerebral cortex is the outer wrinkled layer of the brain responsible for higher cognitive functions.

Scientists use various methods to study brain structure and function:

1. Observing people with brain damage

   • Advantages: Non-invasive
   • Disadvantages: Cannot identify specific brain regions

2. Electrical stimulation (EEG)

   • Advantages: No electricity used, can detect conditions like epilepsy, direct patient feedback
   • Disadvantages: Cannot detect cancer, requires expert interpretation, risk of brain damage

3. MRI scans

   • Advantages: Quick, accurate diagnosis for many conditions
   • Disadvantages: Uses ionizing radiation, risk of allergic reaction to contrast dye

Highlight: Each brain study method has unique advantages and limitations, so researchers often use multiple approaches.

The Eye and Vision

The eye is a complex sensory organ adapted for focusing light to enable vision. Key structures include:

• Cornea: Refracts incoming light
• Pupil: The opening through which light enters
• Iris: Controls how much light enters by adjusting pupil size
• Lens: Further refracts and focuses light onto the retina
• Retina: Contains light-sensitive receptors
• Optic nerve: Carries visual signals to the brain

Vocabulary: The sclera is the tough white outer layer that protects the eye.

The eye adapts to changing light conditions:

• In bright light: Circular muscles contract, radial muscles relax, pupil constricts
• In dim light: Circular muscles relax, radial muscles contract, pupil dilates

The shape of the lens can also be adjusted to focus on objects at different distances.

Example: When you move from a dark room into bright sunlight, your pupils quickly constrict to reduce the amount of light entering your eyes.

Structure and Function of the Human Nervous System

The human nervous system regulates internal conditions and responds to environmental stimuli through homeostasis. Key components include:

• Receptors that detect changes in internal or external conditions
• Coordination centers like the brain and spinal cord that process information
• Effectors such as muscles and glands that produce responses

The nervous system consists of specialized cells called neurons adapted for transmitting electrical impulses:

• Sensory neurons carry signals from receptors to the central nervous system
• Motor neurons transmit signals from the CNS to effectors
• Relay neurons in the spinal cord connect sensory and motor neurons

Definition: The central nervous system (CNS) is the main coordination center that receives sensory information and coordinates responses.

Synapses connect neurons and allow signals to be passed through chemical neurotransmitters. The basic pathway is:

Stimulus → Receptor → Coordinator → Effector → Response

Highlight: Neurons have key adaptations like long axons insulated by myelin sheaths to rapidly transmit signals over long distances.

Reflex arcs provide rapid, automatic responses to reduce injury risk without conscious thought. The steps in a reflex arc are:

1. Receptors detect a stimulus
2. Sensory neurons send signals to relay neurons in the spinal cord
3. Motor neurons transmit signals to an effector
4. The effector (e.g. muscle) produces a response

Example: Quickly pulling your hand away from a hot surface is an example of a reflex action.