The Human Brain: Structure, Function, and Pathways

Posted on May 15, 2024 in Biology

Brain Lesioning

Abnormal disruption in brain tissue resulting from injury/disease.

Electrical Recording

Electroencephalograph (EEG)

Records the brain’s electrical activity.

  • Assess brain damage, seizure disorder, and other problems
  • Key Issue: The cap and electrodes can be difficult to apply to people with curly hair.
  • Has been used to examine brain and happiness.
  • EEG showed that watching amusing clips made people exhibit more left than right activity. 

Electroencephalogram

Electrodes placed on the scalp detect brain-wave activity, which is recorded on a chart called that. 

Brain Imaging

Four techniques that allow scientists to get a picture of the brain are:

Computerized Axial Tomography (CAT/CT)

A three-dimensional image obtained from X-rays of the head, provides info about the location and extent of damage involving store, or loss of memory. Provides info on brain structure but not activity.

Positron-Emission Tomography (PET)

Based on metabolic changes in the brain activity, Provides info about brain activity, tracking glucose in areas of brain and sends this info to a computer for analysis, also used to diagnose diseases.

Magnetic Resonance Imaging (MRI)

Involves creating strong magnetic field around a person’s body and using radio waves to construct images, generates clear pics of brain interior and has no side effects, allows researchers to see if and how experience affects brain structure, doesn’t show brain function. 

Functional MRI (fMRI)

Mental activity is associated with changes in the brain, tells us what specific brain activity is associated with the mental experience being studied, used to establish links between brain areas and behaviors. 

Brain

Hindbrain

  • Medulla Oblongata: Controls breathing, heart rate, and regulates reflexes.
  • Pons: Bridge in hindbrain that connects the cerebellum and the brains stem, contains clusters of fibers involved in sleep and arousal. 
    • Medulla, pons, and much of hindbrain are called brain stem, which connects spinal cord to midbrain. 
  • Cerebellum: Plays important role in motor coordination, leg and arm movements. 

Midbrain

  • Substantia nigra: Contains large amount of dopamine producing neurons, involved in reward experiences, pleasure, and addiction. (Parkinson disease damages this)
  • Reticular formation: Collection of neurons involved in stereotyped patterns of behavior such as walking, sleeping, and turning to sudden noise. 

Forebrain

  • Limbic System: Loosely connected network of structures under the cerebral cortex, it is important in memory and emotions.
    • Amygdala: Involved in detection of objects that are relevant to adaptation and survival, like food, involved in emotional awareness and expression. 
    • Hippocampus: Has a role in memory, helps us recall things by waking up the areas of the brain that were used when originally encountering the information.
  • Thalamus: Relay structure, works to keep things organized and moving to right place, sorts info and sends it to appropriate places for further integration. 
  • Basal Ganglia: Works with cerebellum and cerebral cortex to control and coordinate voluntary movements, enables people to engage in habitual activities like riding a bike.
  • Hypothalamus: Monitors eating, drinking, sex, emotion, stress, and reward, also helps direct endocrine system, its sensitive to changes. 
  • Cerebral Cortex: Where thinking and planning take place. 

Lobes: 

  • Occipital lobes: Respond to visual stimuli, allows for processing of visual stimuli such as color, shape, and motion.
  • Temporal lobes: Involved in hearing, language processing, and memory. 
  • Frontal Lobes: Involved in personality, intelligence, and control of the voluntary muscles. 
  • Parietal Lobes: Involved in registering spatial location, attention, and motor control. 

Somatosensory cortex: Processes info about body sensations.

Moter Cortex: Processes info about voluntary movement.


Association Cortex: Regions of cerebral cortex that integrate sensory and motor information. 

Corpus Callosum: Brain’s two hemispheres connected by a large bundle of axons, the right hemisphere only receives info from the right side of the body and the left only left.

Endocrine System

A set of Glands that regulate the activities of certain organs by releasing their chemical products into the bloodstream. 

Glands: Organs or tissues in the body that produce chemicals that control many bodily functions.

Hormones: Chemical messengers produced by several glands.

Pituitary gland: Controls growth and regulates other glands. 

Adrenal glands: Regulates mood, energy level, and ability to cope with stress.

Pancreas: Produces hormones and insulin.

Ovaries: Female endocrine glands

Testes: Male endocrine glands, both produce hormones involved in sexual development and reproduction.

Characteristics of the Nervous System: 

  • Guides our interactions with the world around us, moves our body through the world.
  • Characteristics that allow the nervous system to direct our behavior: Complexity, Integration, Adaptability, and Electrochemical transmissions.

Complexity: The brain is very complex, the billions of nerve cells allows you to talk, write, sing, dance, and think. 

- The complexity of connections in the brain is its key feature. 

Integration: The brain is good at pulling all the information together. 

Adaptability: The brain and nervous system serve as our agent for adapting to the world, it is constantly adapting to changes in the body and the environment. 

- Plasticity: Brain's capacity for change, when you change the way you think, you change the brain's physical process and its shapes.

Electrochemical transmissions: The way nerve cells or neurons communicate with each other in the body. 

- When a neuron receives a signal, it generates impulse that travels down its length, and when it reaches the end of the neuron, it triggers the release neurotransmitters.

Pathways in the Nervous Systems:

The nervous system has specialized pathways that are adapted for different functions. 

Afferent/Sensory Nerves: Carry information to the brain and spinal cord. 

Efferent/Motor Nerves: Carry info out of the brain and spinal cord. 

Divisions of the Nervous System: 

The Central Nervous System: Brain and spinal cord, 

The Peripheral Nervous System: 

  • Nerves that connects the brain and spinal cord to other parts of the body.

  • Brings info from the brain and spinal cord, and carries out the commands of CNS.

  • Somatic nervous system

    • Sensory nerves, conveys info from the skin and muscles to the CNS about conditions such as pain and temperature.

    • Motor nerves, tells the muscles what to do.

  • Autonomic nervous system: 

    • Takes messages to and from the body’s internal organ. Monitors processes such as breathing, heart rate, and digestion.

      • Sympathetic Nervous System: Arouses the body to mobilize it for action, Fight or flight response, body’s reaction to a threat.

      • Parasympathetic Nervous System: Calms the body after escaping danger, rest and digest.

Neurons

  • Two types of cells in the nervous system: neurons and glial cells. 

  • Glial cells: Provide support and nutrition, keeps neurons healthy and insulated. 

    • Serves as the brains immune system, maintains water ratio and balance in the chemical aspects of N.S.

    • Are able to repopulate themselves.

  • Neurons: Nerve cells that handle information processing.

    • Mirror Neuron: Imitation, Social perception, when someone yawns, you yawn, activated when you perform an action or observe someone else performing it.

Neuron Structure:

  • Every neuron consists of a cell body, dendrites, and an axon. 

    • Cell body: Contains nucleus which directs the manufacture of substances that the neuron needs for growth and maintenance.

    • Dendrites: Receive info and orient it toward the neuron’s cell body.

    • Axon: Carries info away from the cell body toward other cells. 

  • Myelin Sheath: Layer of cells containing fat, encases and insulates most axons which speeds up transmission of nerve impulses, lack of this can cause Multiple Sclerosis. 

Neural Impulse/Action Potential: 

  • At rest, the inside of a neuron is composed of negatively charged ions, and the outside has positive ions, 

  • When activated, gates along the cell membrane open and allows positively charged ions to flow into the neuron, so many sodium ions rush in that for a brief moment, the neuron has a positive charge.

  • This sweeps down the axon as the channels open and then close, this is called action potential.

  • As the impulse passes through a section of the axon, the neuron will return to a negative charge, this same process occurs all the way down the axon. 

  • All-nothing principle: Once the electrical impulse reaches a certain level of intensity, called its threshold, it fires and moves all the way down axon without losing any of its intensity.

Synapses and Neurotransmitters:

  • Electrochemical transmission: Neurons communicate with each other through chemicals that carry messages across the space if the neurons don’t touch.

  • Neurotransmitters: Chemical messengers that transmit signals between neurons in the nervous system.

Synaptic Transmission:

  • Synapses are tiny spaces between neurons and the space between neurons that synapses create is called synaptic gap. 

Drugs and Neurotransmitters

  • Drugs can mimic or increase the effects of a neurotransmitter, or they can block those effects.

  • E.g.: The drug morphine mimics the actions of endorphins by stimulating receptors in the brain and spinal cord associated with please and pain, producing feelings of pleasure. 

Neural networks:

  • Most information processing occurs when info moves through neural networks-interconnected pathways of nerve cells that integrate sensory input and motor output.