Mental activitiesMental activities

The Brain-Nerve NetworkThe Brain-Nerve NetworkBrain

◦Control center for the body◦Requires a continuous flow of oxygen

and blood, 20 % of COParts of the brain

◦Cerebrum Left and right hemispheres

Frontal lobe – skilled motor behavior; speech, mood, thought, planning

Parietal lobe – interprets sensory info controls body movement

Occipital lobe – vision Temporal lobe – memory and emotions, long term

memories, initiates communication and actions

The Brain-Nerve NetworkThe Brain-Nerve NetworkNerve cells at the base of the cerebrum:

◦Basal ganglia – smooth out movements◦Hypothalamus – coordinates automatic

functions of the body Sleep/wakefulness, body temp, water

balance◦Thalamus – organizes sensory messages

to and from the cerebrum

The Brain-Nerve NetworkThe Brain-Nerve NetworkParts of the brain

◦Cerebellum Coordinates the body’s movements

◦Brain stem Regulates body functions –body posture,

breathing, swallowing, heartbeat, increases alertness

Damage causes deathSpinal cord

◦Pathways for nervous signals and reflexes

◦Protected by vertebral column◦Afferent nerves = motor = ventral◦Efferent nerves = sensory = dorsal

The Brain-Nerve NetworkThe Brain-Nerve NetworkNerve impingements

◦Displacements of vertebrae and material from ruptured vertebrae can inhibit nervous signals

◦Motor nerve damage consequences?◦Sensory nerve?

Neurons – the basic functional unit of the nervous system◦1 billion within the NS◦3 sections:

1. Cell body/ soma2. Dendrites – receives signals3. Axon – transmits signals

The Brain-Nerve NetworkThe Brain-Nerve NetworkSignal transmission

◦Synapses as transmitters and filters/switches

◦Signal amounts vary, 25-1000 impulses/ sec

◦Transmission speed varies among neurons depending on thickness and myelination 0.5 – 150 m/s Velocity is constant for each individual fiber Slow transmission for pain fibers, fast for

muscle innervation

The Brain-Nerve NetworkThe Brain-Nerve NetworkAction potential

◦Electrical spike generated when the stimulus reaches threshold

The Brain – Nerve NetworkThe Brain – Nerve NetworkMotor unit – consists of a motor

neuron and the muscle fibers it innervates◦Muscles involved in precise

movements have 1 MU per 3-6 muscle fibers, heavy work muscles may have 1MU per 100 fibers

◦Motor endplate – point where the motor neuron ends and the NMJ is formed, impulse leaps from the neuron to the muscle fiber

The Brain-Nerve NetworkThe Brain-Nerve NetworkEMGs

◦Records the electrical activity in a muscle

◦Electric current is picked up via electrodes inserted into the muscle or attached to the surface of the skin

◦Observe strength and frequency of muscle activation and status of fatigue

◦Useful in studying individual muscle contribution to maintaining posture

The Brain-Nerve NetworkThe Brain-Nerve NetworkFeedforward/feedback loop

◦ Stretch receptors—two types; muscle spindles and Golgi tendon receptors operate to provide body with information concerning muscle length and strength of muscle contraction

Muscle spindle—composed of 5 to 10 intrafusal fibers lying between and parallel to regular (extrafusal) muscle fibers If length of a muscle exceeds a certain limit, a stretch

reflex is initiated to shorten the muscle, thus helping to maintain posture

Golgi tendon organs—located at junction between muscle tissue and tendon Transmit sensory impulses to the cord whenever the

tendon is under tension Golgi tendon reflex protects muscle from tearing

internally as a result of excessive contractile force Reflex arc – system of an afferent sensory nerve and

efferent motor nerve of the same muscle to keep tension and length constant Muscle spindle and GTO = detectors within this system

The Brain-Nerve NetworkThe Brain-Nerve NetworkDesign for simple movement control

◦Muscle activities involving fine regulation requires involvement of high brain centers

◦Learning complex movements is difficult and slow

◦Human factors engineers need to design activities in the simplest way Least decision making Using fastest path of info transmission Using smallest body mass

The Brain-Nerve NetworkThe Brain-Nerve NetworkThe brain is the control center

which communicates with the body via nerves moving up and down the spinal cord

Sensory nerves relay info about pressure, pain, heat, cold, vibration, feel, body part position (GTO and muscle spindles)

The brain integrates the information and makes decisions

The Brain-Nerve NetworkThe Brain-Nerve NetworkReflexes

◦Spinal cord is also a source for coordination of movements

◦Sensory receptor stimulation message sent to SC immediate response to the appropriate muscles

◦Reaction occurs in a few milliseconds because there is no higher brain function necessary

The Brain-Nerve NetworkThe Brain-Nerve NetworkCNS and PNS

◦CNS – brain and spinal cord Controls the body by gathering information,

making decisions and initiating actions

◦PNS – sensory (afferent) and motor (efferent) divisions Somatic nervous system – controls conscious

actions and mental activities; links organism to environment

Autonomic Nervous system – controls internal organs and mechanisms essential for functioning Parasympathetic vs sympathetic

The Brain-Nerve NetworkThe Brain-Nerve NetworkSensory receptors

◦ Nervous system monitors all sensations◦ If the signal is strong enough, info is transmitted to

the CNS where it is integrated and an appropriate response is elicited

External receptors◦ 5 senses◦ Different kinds of nerve sensors are embedded in

the skin in varying concentrations◦ Dermatome: region of skin surface area supplied

by efferent (sensory) fibers of a given spinal nerve◦ Certain areas have less dense concentrations of

receptors than others

Taking up InformationTaking up InformationProcessing Information

◦Sense info, process it, act on it◦Figure 9.9 Linear processing of signals◦Sensory feedback loop compares the

output of the system to the desired performance and makes the appropriate adjustments

Sensors inside the body◦Interoreceptors – GTO, semicircular

canals, aortic arch pressure receptors

Taking up InformationTaking up InformationSensors near the surface

◦Exteroreceptors – involved in sight, sound, taste, smell, touch; also control body activities by providing feedback regarding the intensity and direction of muscle activities

◦Sensors are located in different densities throughout our body

◦Most common are free nerve endings, Meissner’s and Pacinian corpuscles

Taking up InformationTaking up InformationAdaptation and speed

◦Sensors respond quickly to stimulus, but report less info when the load remains constant

◦Adaptation allows us to filter out unimportant stimuli

◦Speed of adaptation and velocity of signal transmission varies with sensors

Taking up InformationTaking up InformationModifying input signals

◦Humans cannot perceive certain signals

◦An ergonomic task is to modify external signals which we are not able to sense but are important to us

◦In some cases we need to adjust the signal or change the environment so the signal can penetrate a cluttered environment

Making DecisionsMaking DecisionsModels of information processing

◦Model of mental work Evaluation Execution Resulting new environment is reevaluated

◦Multiple sources of info are present and being evaluated simultaneously Our mind filters and transforms info from

previous stages, integrates it and compares it to previous memories

Cognitive ability depends on: the number of stages required and the efficiency of operations at each stage

Making DecisionsMaking DecisionsPerception of sensory signals

◦First stage is to select the info to be further processed

◦The brain compares new inputs to memory, searching for familiar features

◦We use past experiences to generate future expectations

◦New sensory input can either be rejected, or we just may not know what to do with it

Making DecisionsMaking DecisionsShort term memory

◦AKA working memory◦Registers information for a brief moment

(1sec)Long term memory

◦No duration constraints◦General knowledge = semantic memory;

specific events = events memory◦Forgetting is due to never having the info

successfully stored or lacking the proper queues

Making DecisionsMaking DecisionsLong term memory (cont.)

◦Recalling information stored in long term memory may occur by associations with similar situations in the past

◦2 things influence if the info is available:1. The strength of the information trace - depending

on the initial importance, number of times activated and how recently it occurred

2. Association with related items or events

Making DecisionsMaking DecisionsAKA central processingMust understand outcomes of

several different responses and recognize which activities are needed to execute the responses

Shrinking the IP requirements, using limited inputs and integration makes tasks easier

Making DecisionsMaking DecisionsFitting the human to the job

◦People need experiences to compare information coming into the CNS

◦Comes with aging, teaching an training

New models of IP◦Current concept is based on the

computer metaphor◦Advanced concepts base models on

neurophysiology

Actions and ReactionsActions and Reactions

Direct task – hammer, screw driverTransduced task – a piece of

machinery is used to modify the action of the body

The design of the transducers and their feedback is a challenge to human factors engineers

Actions and ReactionsActions and ReactionsResponse time

◦Time from the appearance of a stimulus to the beginning of an effector action

◦Response time = reaction time + motion timeReaction time

◦Time delays from the appearance of the signal to action: receptor 1-38 ms Afferent path 2-100 ms CNS processing 70 – 100 ms Efferent path 10 – 20 ms Muscle latency and contraction 30 -70 ms

Actions and ReactionsActions and ReactionsSimple reaction times

◦Occurs when a person is prepared for a particular stimulus

◦Duration depends on kind of stimulus and intensity

◦Change little between 15 – 60 years, but are slower at younger ages and decline with age

Actions and ReactionsActions and ReactionsChoosing between reactions

◦Choice reaction time – longer than a simple reaction time and increases if multiple similar stimuli are available to choose from

Motion time◦Simple or complex◦Depends on distance of movement

and required precision

Actions and ReactionsActions and ReactionsHuman factors concerns

◦Minimize response time◦Optimizing the stimulus◦Selecting the most appropriate body

part◦Careful task selection◦Assessment of individual capabilities