Biological Basis of Behavior: The Nervous System

Biological Basis of Behavior: The Nervous System 1. 2. Structure of the Nervous System: 2 Main Nervous Systems: Central and Peripheral Nervous System CNS includes the brain and spinal cord For the brain: Midbrain: which has the midbrain, pons, and medulla oblongata Cerebellum: portion in the back of the brain important for voluntary movements such as posture, balance, coordination, and speech which results in smooth and balanced muscular activity Important to note that prosencephalon = forebrain, mesencephalon = midbrain, and the rhombencephalon = hindbrain Afferent (Sensory) Neurons: carry information into the CNS and carry information through the dorsal root (posterior nerves) Efferent (motor) Neurons: carry information away from the CNS and carry information through the ventral roots (anterior nerves) Functions of the Nervous System: Syndromes: patterns of abnormal behavior within the nervous system Basic (Lower) Function: motor (skeletal) movement, sensory functions, and automatic functions (dont require conscious involvement such as reflexes) Complex (Higher) Functions: not really performed by huge areas of the central/peripheral nervous systems and are performed by the brain. A couple different categories that include cognition (thinking functions of the brain), emotions (feelings), and consciousness (awareness of being a person) Motor Unit: Lower Motor Neurons: synapse on skeletal muscle in order to regulate its movement through contraction The motor unit involves the lower motor neuron and all the skeletal muscle cells (muscle fibers) with which it innervates. This allows ALL the muscle cells with which it innervates to contract together and work as a unit Typically where a neuron meets a cell is known as a synapse but in the case of a motor unit it is known as the neuromuscular junction Within the somatic nervous system there is a single nerve which goes out to its effector organs whereas in the autonomic nervous system there are two nervous (a preganglionic nerve and a postganglionic nerve) Smaller motor units are used for areas of the body that have smaller muscles and therefore need more precise control (such as the eyes and the hands) whereas the larger motor units are used for areas of the body that have larger muscles and do not need precision with their movement (such as the muscles of the legs) What happens when motor units form abnormalities? Atrophy: lower bulk of muscles Fasciculations: involuntary twitches of skeletal muscles Hypotonia: decrease of skeletal muscle tone (which is how much muscle is contracted when the person is trying to relax it) Hyporeflexia: decreased muscle stretch reflexes Peripheral Somatosensation: Somatosensation: senses of the body and there are 5 main ones: Position Sense: position of body parts relative to one another Vibration Sense: we can feel vibrations if it is vibrating Touch Sense: feel touch Pain Sense: feel pain Temperature Sense: feel changes in temperature A couple of different types of receptors for somatosensation: Mechanoreceptors: respond to physical forces and mechanical stimuli (i.e. position, vibration, and touch - even muscle stretch!) and typically have a structure found at the end of the axon Nociceptors: respond to stimuli which invoke pain - do not typically have a structure at the end of its axon like mechanoreceptors do Thermoreceptors: detect temperature - do not typically have a structure at the end of its axon like mechanoreceptors do Important note: the increase of diameter axons allows APs to travel faster while smaller diameter axons give rise to slower action potentials In this case, position, vibration, and touch senses travel through larger diameter/myelinated axons while pain, temperature, and other touch senses travel through smaller diameter/myelinated/unmyelinated axons Muscle Stretch Reflex: Reflex: response to a stimulus that doesn’t require the involvement of consciousness and have 2 parts Afferent Part: bringing information INTO the CNS, AKA somatosensory neurons Efferent Part: brings information away from the CNS to cause a response in the periphery, AKA lower motor neurons Muscle Stretch Reflex: ipsilateral reflex, if a muscle is rapidly stretched, it will cause it to contract very quickly (likely as a protective response) and this is what happens when your doctor hits you with a rubber hammer below your kneecap (known as the patellar reflex or the knee-jerk reflex) The receptors that respond to the stretch are known as muscle spindles If there is an issue with either the efferent or afferent part of the reflex can lead to a decreased response to a reflex Other motor neurons can inhibit other muscles (such as in the knee-jerk reflex it will cause the muscle under the leg to relax) - - Autonomic Nervous System: The ANS controls efferent neurons which control: smooth muscle, cardiac muscle, and some gland cells The ANS does not need conscious involvement and acts autonomously 2 Big Subsystems of the ANS: Sympathetic Nervous System: starts in the middle section of the spinal cord and hence why its called the thoracolumbar nervous system (shorter preganglionic neuron and a longer postganglionic neuron) - “fight or flight” (i.e. blood flow is redirected away from the intestines therefore decreasing energy wasted here) and also works with sweat glands Parasympathetic Nervous System: starts in the extremity portions of the spinal cord and hence why its called the craniosacral nervous system (longer preganglionic neuron and a shorter postganglionic neuron) - “rest and digest” (i.e. blood flow is directed here to the intestines because we don’t need much energy elsewhere) Grey and White Matter: Grey Matter: contain neuronal cell bodies (somas) White Matter: contain axons The Spinal Cord has most of its grey matter on the inside and white matter on the outside (butterfly shape) The Brain has most of its grey matter on the outside and white matter on the inside The layer of grey matter on the outside of the brain is known as the cortex - - - Cerebral Cortex: grey matter covering the cerebrum (outside layer) Cerebellar Cortex: grey matter covering the cerebellum (outside layer) Nuclei: areas of grey matter deep within the cortex Tracts: areas of white matter (axons) in the CNS Upper Motor Neurons: Remember, lower motor neurons have their somas that originate in the brainstem or spinal cord that go out to the peripheral to control skeletal muscle cells Upper Motor Neurons: control these lower motor neurons and their activity, and they are also found mainly in the cerebral cortex that have axons that go down to the lower motor neurons (they are typically contralateral and cross over to the other side once they reach the spinal cord) Corticospinal Tract: when upper motor neurons travel from the cerebral cortex to the spinal cord (typically contralateral) Corticobulbar Tract: for the tracts that go from the cerebral cortex to lower motor neurons in the head, they typically are either ipsilateral or contralateral Weakness in muscle contraction can be fault of both the lower and upper motor neurons Upper Motor Neuron Signs: Hyperreflexia: increase in the muscle stretch reflex Clonus: rhythmic contraction of antagonist muscles (meaning that the antagonist muscle will stretch along with the agonist muscle) Hypertonia: increase muscle tone Extensor Plantar Response: typically individuals show a flexor plantar response but individuals with upper motor neuron issues, then the foot will plantar extend (AKA babinski sign) shown on the right → Somatosensory Tracts: If there is injury to one side of the brain, the other side of the body will show somatosensory loss 1. 2. 3. Cerebellum: Cerebellum: coordinates movement (smooths them out and makes them more accurate) 3 Parts to how information coordinates movement: Motor Plan: which muscles need to contract and what intensity/duration in order to do some sort of movement Position Sense Information: unconscious information that goes directly to the cerebellum, receptors take information from the body part moving to the cerebellum (basically a correction) Feedback: sends feedback back to the motor areas of the cerebrum in order to fix the movement to make it smoother and more accurate The middle of the cerebellum helps most with moving middle parts of the body (trunk and legs involved in things like walking) while the lateral sections are more important in movement of arms/legs when they move individually, and a bunch of portions of the cerebellum are involved in speech production and eye movement Brainstem: The brainstem works to connect all of the different parts of the nervous system together and most of the cranial nerves are attached to the brainstem Reticular Formation: neuronal somas scattered about the brainstem sections and plays a huge role in autonomic functions and plays a big role in circulation, respiration, and even digestion; it even plays a role in a lot of higher cognitive functions 2 main categories of long tracts passing through the brainstem (motor tracts and somatosensory tracts) Subcortical Cerebrum: Internal Capsule: a white matter structure that passes through the cerebrum (has the corticospinal tract pass through it) Corpus Callosum: the biggest and most important tract that allows information to travel from one cerebral hemisphere to another Basal Nuclei (Ganglia): located on the interior of the cerebrum and play an important role in motor functions (don’t have motor neurons but help the upper motor neurons), cognition, and even emotion Thalamus: also known as the diencephalon and plays a very important role in sensory functions (because almost all senses except smell pass through the thalamus before heading up to the cerebral cortex) and is important in a lot of the higher functions of the brain Hypothalamus: connected to and controls the pituitary gland which is the major gland in controlling the endocrine system and acts as a link between the nervous system and the endocrine system Cerebral Cortex: Cerebral Cortex: layer of grey matter on the outside of the cerebrum and contains the frontal lobe, parietal lobe, temporal lobe, and occipital lobe Gyri: ridges in the cerebral cortex Sulci: folds in the cerebral cortex and larger sulci are known as fissures Information coming in from one side of the body will be processed on the opposite side of the cerebral cortex (primary somatosensory and visual information) Motor information will also exhibit contralateral behavior Primary Cortex: performs basic motor or sensory functions Association Cortex: associates different types of information in order to perform more complex functions (like planning) Most people have language function just on the left cerebral hemisphere known as Broca’s area (frontal lobe) and Wernicke’s area (temporal lobe) Neurotransmitter Anatomy: Neurotransmitters: act at synapses and are molecules that allow neurons to communicate with one another Glutamate: most common excitatory neurotransmitter of the entire nervous system GABA: inhibitory neurotransmitter (particularly in the brain) Glycine: inhibitory neurotransmitter (particularly in the spinal cord) Reticular Activating System: required for consciousness, without this there is none (release glutamate to neurons all over the cerebral cortex) Acetylcholine: basalis and septal nuclei release acetylcholine to the cerebral cortex Histamine: neurons in the hypothalamus release this neurotransmitter into the cerebral cortex Norepinephrine: area in the pons (locus coeruleus) that has neurons which send norepinephrine to areas of the cerebral cortex Serotonin: areas in the midbrain, pons, and medulla (raphae nuclei) release serotonin to the cerebral cortex Dopamine: area in the midbrain responsible for releasing dopamine to the cerebral cortex (ventral tegmental area - VTA) and the substantia nigra is important for dopamine release to the basal nuclei (ganglia) deep within the brain (issues with this can lead to Parkinson’s disease) - Lastly, the hypothalamus has important functions with dopamine release in order to control other hormone release of the pituitary gland Many different diseases are related to issues with neurotransmission within the brain Early Method of Studying the Brain: Cerebral Localization: the idea that specific portions of the brain perform specific functions Lesson Studies & Experimental Ablation: Alation: deliberately destroying brain tissue in order to study its effects on function or behavior (done on animals), this can be done through surgical removal/aspiration, radiofrequency lesions (used to destroy tissue on surface of brain or deep within the brain and uses a wire to pass radio waves to heat up to destroy everything within that area), neurochemical lesions (excitotoxic lesions which attach to glutamate receptors that cause such a high influx of calcium that it kills it and is more specific and oxidopamine is used to be sucked back up into the neuron and kill the neurotransmitters within it), and cortical cooling (cooling neurons until they simply stop firing and is the only temporary technique listed) - - - Modern Ways of Studying the Brain: Methods that study Brain Structure: CAT/CT Scans: uses X-rays to create an image of the brain, can tell if there is a tumor or abnormal swelling or bleeding but it doesn’t tell much about what areas of the brain are active at a given time MRI: uses radio waves to create an even more detailed image of the brain but still doesn’t tell us anything about brain function Methods that study Brain Function: EEG: measures the electrical activity generated by neurons in the brain by placing electrodes on the scalp (non-invasive) but can’t tell you specifically which neurons/cells aren’t working/are, it just gives you an overall picture of what is going on (and we don’t get a picture of the brain but instead a whole bunch of graphs with waves given off by the brain) MEG: measuring magnetic fields produced by the electrical currents within the brain and has better resolution that an EEG but is more rare since it needs a lot more extra fancy equipment Methods that study Both Brain Structure & Function: fMRI: this gives you the ability to see structure (like in the MRI) but also activity of the different brain structures (since active neurons require oxygen, then measuring relative oxygen amounts we can see what areas of the brain are located) PET Scans: on their own they can’t give structural information, but you can pair them with other techniques and radioactive glucose is injected into the patient and you can tell where this glucose is being used at (invasive option)`