Student Library

3.4 The Brain and the Spinal Cord

8 min read

The Spinal Cord

  • connects the brain to the outside world.
  • acts as a relay station and houses automatic processes, called reflexes.

Structure of the Spinal Cord

  • The top of the spinal cord are a bundle of nerve that merges with the brain stem.

  • The spinal cord ends just below the ribs.

    • It does not extend all the way to the base of the spine.

  • The spinal cord is organized into 30 segments

    • This corresponds to the number of vertebra in the spine.

  • Each segment is connected to a specific part of the body through the PNS.

    • Nerves branch out of the spine at each vertebra
      • Sensory nerves bring messages in toward the brain.
      • Motor nerves send messages out to the muscles and the organs.

Reflexes

  • Some sensory messages are processed by the spinal cord without direct input from the brain.
    • When a sensory message meets certain conditions, the spinal cord initiates an automatic reflex.
    • The signal passes from the sensory nerve to a simple processing center which initiates a motor command.
    • This is valuable as it allows the body to respond faster in matters of survival as messages doesn’t have to go all the way to the brain to be processed and sent back.

Protection and Damage

  • The spinal cord is protected by bony vertebra and cushioned with cerebrospinal fluid.
    • When injuries occur in the spinal cord, all lower segments are cut off from the brain, which causes paralysis
    • The higher on the spine damage occurs, the more functions an individual will lose

Neuroplasticity

  • refers to how the nervous system can change and adapt though personal experiences, developmental processes in response to injury or damage occurred.
  • it can involve:
    • creation of new synapses,
    • removing synapses that are no longer used,
    • changes in glial cells,
    • and the creation of new neurons.
  • The nervous system is most plastic when we are young, though it is still capable of remarkable changes later in life.

The Two Hemispheres

The Surface of the Brain and its Structure

  • The surface of the brain is known as the cerebral cortex.
    • It’s described by a distinctive patterns of uneven bumps or folds (known as gyri), and grooves (known as sulci)
    • The largest sulcus is the longitudinal fissure.
      • This deep groove divides the brain into the left and right hemispheres.
  • The two hemispheres are connected by the corpus callosum.
    • This is a thick band of neural fibers that contains 200 million axons.
    • It allows both hemispheres to communicate and share information to be processed on the other side.

Specialization of a Hemisphere

  • There are evidences that one hemisphere is more specialized in a certain area than the other.
    • This is called lateralization of function.
    • For example, the left hemisphere has shown to be superior in forming associations in memory, selective attention, and positive emotions.
      • The right hemisphere is shown to be superior in pitch perception, arousal and negative emotions.
    • One more example is that research shows that the left hemisphere controls the right half of the body, and the right hemisphere on the left half of the body.
  • However, research on which hemisphere is superior has produced inconsistent results.
    - Therefore, it is better to think how the two hemispheres interact instead of attributing behaviors to just one hemisphere

How Scientists Study the Brain’s Functions

  • By studying people who suffered some damage to the brain, researchers were able to study the functions of the brain’s different areas.
    • For instance, studying behavioral changes caused by strokes allowed them to determine the function of specific brain areas.
    • A stroke is a loss of brain function in the a region caused by an interruption of blood flow to that affected region in the brain.
    • Studying damages to a specific area in the brain give researchers an opportunity to link any resulting behavioral changes to that specific area.

Forebrain Structures

  • The forebrain constitutes the two hemispheres of the cerebral cortex.

    • It is also the largest part of the brain.
    • It also contains some structures beneath the cerebral cortex.
      • These are called subcortical structures.
      • They are composed of:
        • thalamus
        • hypothalamus
        • pituitary gland
        • limbic system

  • The cerebral cortex is associated with higher-level processes such as:

    • consciousness
    • thought
    • emotion
    • reasoning
    • language
    • memory

Lobes of the Brain

  • Each cerebral hemisphere can be subdivided into four lobes:
    • frontal lobe
      • the forward part of the brain
      • extends back to a fissure in the central sulcus
      • it contains the:
        • motor cortex: for planning and coordinating movement
        • prefrontal cortex: for higher-level cognitive functioning
        • Broca’s area: for language production
          • any damage in this area will prevent them to produce any meaningful language (either through writing or speaking)
    • parietal lobe
      • located immediately behind the frontal lobe
      • involved in processing information from the body’s senses
      • it contains the somatosensory cortex:
        • this part of the brain processes touch and sensation
        • each part of the cortex processes a different part of the body.
        • the larger the surface area of a body part and the greater number of nerves in that part, the larger the area dedicated to processing sensation from that area in the somatosensory cortex.
    • occipital lobe
      • located at the very back of the brain
      • contains the primary visual cortex
        • responsible for interpreting visual information
    • temporal lobe
      • located on the side of the head (temporal near the temples)
      • associated with hearing, memory, emotion, and some aspects of language
      • contains the:
        • auditory cortex: responsible for interpreting auditory information
        • Wernicke’s area: responsible for speech comprehension
          • damage in this area can produce language, but they are unable to understand it.

Other Areas of the Forebrain

  • Thalamus ^thalamus
    • a sensory relay for the brain.
    • all sensory information (except smell) are routed through the thalamus before redirected to other areas of the brain for processing
  • Limbic System
    • involved in processing emotion and memory
    • area in the brain where the sensory information for smell goes
    • made up of important structures, such as:
      • hippocampus: essential for learning and memory
      • amygdala: involved in experience of emotion and tying emotional meaning to our memories
      • hypothalamus: ^hypothalamus
        • regulates homeostatic processes
        • serves as an interface between the nervous system and endocrine system
        • responsible of regulation of sexual motivation and behavior

The Midbrain and the Hindbrain

  • Midbrain

    • comprised of structures located deep within the brain, between the forebrain and the hindbrain
    • these structures are:
      • reticular formation:
        • at the middle of the midbrain
        • extends up into the forebrain and down into the hindbrain.
        • regulates sleep/wake cycle, arousal, alertness, and motor activity
      • substantia nigra and the ventral tegmental area (VTE)
        • contains cell bodies that produce the neurotransmitter dopamine
        • critical for movement and involved in mood, reward, and addiction.

  • Hindbrain

    • located at the back of the head
    • composed of:
      • medulla:
        • controls the automatic processes of the autonomic nervous system
      • pons ^pons
        • means “bridge”
        • connects the hindbrain to the rest of the brain
        • regulates brain activity during sleep
        • along with the medulla and some other structures, they comprise of the brainstem
      • cerebellum
        • controls balance, coordination, movement and motor skills by receiving messages from the muscles, tendons, joints, and structures in the ear.
        • also an important area in processing procedural memory, memory involved in learning and remembering how to perform tasks

Brain Imaging Techniques

  • Computerized Tomography (CT) scan
    • it involves taking a number of x-rays of a particular section of a person’s body or brain.
      • The computer then constructs an overall image of the area being scanned by based on how fast an x-ray passes through the tissues
    • allows them to determine whether someone has a tumor or brain atrophy
  • Positron Emission Tomography (PET) scan
    • creates pictures of the living, active brain by tracing the amount of radioactive substance, called a tracer, in the bloodstream
      • this radioactive substance is introduced via ingestion (drinking) or injection.
    • the computer then monitors the movement of the tracer and creates a map of active and inactive areas of the brain based on the blood flow.
      • more blood flow = more activity in the area of the brain
    • in short, PET scans provide information about the brain activity during a given behavior.
      • often combined with CT scans to provide better imaging of neurotransmitter receptor activity in schizophrenia research
  • Magnetic Resonance Imaging (MRI)
    • a person is placed inside a machine that generates a strong magnetic field, which causes hydrogen atoms in the body to move
    • upon turning the magnetic field off, hydrogen atoms return to their original positions and emit electromagnetic signals.
    • the signals then pass through tissues which give off different signals based on their density
    • this information is the interpreted by the computer and then displays the image into the monitor
    • Functional magnetic resonance imaging (fMRI) operates the same way, but records brain activity over time by tracking blood flow and oxygen levels.
      • It also provides more accuracy in time than PET scans.
  • Electroencephalography (EEG)
    • an array of electrodes placed around a person’s head measures the brain’s electrical activity.
    • the signals received are then printed out, showing the frequency and amplitude of the electrical activity (brainwaves) over time.
    • this allows researchers to study sleep patterns on individuals with sleeping disorders

Graph View